A by-product is an incidental product from a process which has an _______ value compared to the main products.

A、A product produced at the same time as other products which has no value

B、A product produced at the same time as other products which requires further processing to put it in a saleable state

C、A product produced at the same time as other products which has a relatively low volume compared with the other products

D、A product produced at the same time as other products which has a relatively low value compared with the other products

As more people live closer together, and as they use machines to produce leisure, they find that their leisure, and even their working hours, become spoilt by a by-product of their machines--namely, noise. Noise is nowadays in the news; it has acquired political status, and public opinion is demanding, more and more insistently, that something be done about it. So it was very appropriate' that many people professionally interested in noise control should meet to discuss their common problems at a large-scale conference. In the three days of the Conference at Teddington, 25 papers were presented; and faced with the pile of texts, whose contents ranged from sophisticated aerodynamics to general comments on the irritation expressed by neighbours, it was difficult to sort out the new ideas which remain active in one's mind six months from now, from the big mass of valuable knowledge and facts which will remain on the shelves for reference.

This difficulty was faced by Mr. D. W. Robinson, head of the acoustics work at the National Physical Laboratory. His introduction elaborated the general idea that noise must be considered in relation to the social organism which produces it. Sound becomes annoying noise only when someone's opinion has made it so. In terms of energy, it is an undesired byproduct, often an exceedingly small fraction of the main output of the machine or process which produces it, and correspondingly difficult to reduce significantly. To control noise is going to demand much self-discipline (annoyance arises often from lack of common courtesy and imagination), a sense of proportion (there is usually a conflict of interest if a noise is to be stopped), the expenditure of money (and it is far more economical to do this early rather than late), and, finally, technical knowledge.

Technical difficulties often arise from the subjective-objective nature of the problem. You can define the excessive speed of a motor Car in terms of a pointer reading on a speedometer. But can you define excessive noise in the same way? The results of several large-scale experiments, involving numbers of vehicles and of listeners, show how difficult it is to fix any instrumental reading as a legal limit in a way which satisfies most of the public and yet is fair to the vehicle owner. You, find, for example, that with any existing simple "noise meter", vehicles which are judged to be equally noisy by a jury may show considerable difference on the meter.

A group of papers dealt with noise, at the source--the basic origins of noise in gears, internal combustion engines, fans and jets. The prospect of a significant reduction in noise output from jet engines of the future was one of the most important questions discussed at the conference. Though the ideal cure for noise is to stop it at its source, this may in many cases be impossible. The next weapon in the anti-noise armory is to absorb it in transit to the ear.

It is a common fallacy that a sound absorbent such as glass wool is opaque to sound and is therefore the best way of diminishing annoying noise from the flat next door. In a normally furnished room, lining a wall with absorbent will have little effect on the noise level built up by reverberation; and will contribute hardly anything to the acoustic opacity of the wall. In a typical factory building, even if all available surfaces are covered with absorbent, the noise level is unlikely to drop by more than five decibels. A consultant will often recommend light partitioning, and partial screening round noisy machines, as a more of the Conference at Teddington, 25 papers were presented; and faced with the pile of texts, whose contents ranged from sophisticated aerodynamics to general comments on the irritation expressed by neighbours, it was difficult to sort out the new ideas which remain active in one's mind six months from now, from the big mass of valuable knowledge and facts which will remain

A．They refer to the objective and subjective nature of the problem respectively.

B．Noise is dispensable in terms of energy but it is indispensable in sociological terms.

C．Noise is hard to control in terms of energy while it may be controllable in sociological terms.

D．All of the above.

1.Helen is worried about food safety.

2. So far, the contaminated baby milk hasn't caused any deaths yet.

3. Food incidents occur not as often nowadays as before.

4. Food safety is an old problem.

5. Public confidence in the milk industry will be back soon.

A by B up C about D to

Nowadays, more people are living closer together, and they use machines to produce leisure. As a result, they find that their leisure, and even their working hours, become (1)_____ by a byproduct of their machines, (2)_____ noise. Noise is in the news; it has acquired political (3)_____, and public opinion is demanding, more and more (4)_____, that something (5)_____ about it.

To control noise is to demand much (6)_____(Annoyance arises often from, (7)_____ of common courtesy), a sense of proportion (There is usually a (8)_____ of interest if a noise is to be stopped), the (9)_____ of money (and it is far more economical to do this early (10)_____ than late), and, finally, technical knowledge.

Though the (11)_____ care for noise is to stop it at its source, this may in many (12)_____ be impossible. The next (13)_____ is to absorb it on its way to the ear. Domestic noises may be controlled by forethought and (14)_____, and industrial noises by good planning and technical (15)_____ But if we are going to (16)_____ fast motor-cycles and heavy (17)_____ lorries to pass continuously through residential and business (18)_____, the community must decide (19)_____ the control it needs to (20)_____ for in the long run it has got to pay for it.

A．damaged

B．spoilt

C．destroyed

D．interfered