The EMF induced in a circuit is equal to the magnetic flux through the circuit.

The relationship between the home and market economies has gone through two distinct stages. Early industrialization began the process of transferring some production processes (e.g., cloth making, sewing and canning foods) from the home to the market place. Although the home economy could still produce these goods, the processes were laborious and the market economy was usually more efficient. Soon, the more important second stage was evident—the marketplace began producing goods and services that had never been produced by the home economy, and the home economy was unable to produce them (e.g., electricity and electrical appliances, the automobile, advanced education, sophisticated medical care). In the second stage, the question of whether the home economy was less efficient in producing these new goods and services was irrelevant; if the family were to enjoy these fruits of industrialization, they would have to be obtained in the marketplace. The traditional ways of taking care of these needs in the home, such as in nursing the sick, became socially unacceptable (and, in most serious cases, probably less successful). Just as the appearance of the automobile made the use of the 'horse-drawn carriage illegal and then impractical, and the appearance of television changed the radio from a source of entertainment to a source of background music, so most of the fruits of economic growth did not increase the options available to the home economy to either produce the goods or services or purchase them in the market. Growth brought with it increased variety in consumer goods, but not increased flexibility for the home economy in obtaining these goods and services. Instead, economic growth brought with it increased consumer reliance on the marketplace. In order to consume these new goods and services, the family had to enter the marketplace as wage earners and consumers. The neoclassical model that views the family as deciding whether to produce goods and services directly or to purchase them in the marketplace is basically a model of the first stage. It cannot accurately be applied to the second stage.

The reason why many production processes were taken by the marketplace was that ______.

A．it was a necessary step in the process of industrialization

B．they depended on electricity available only to the market economy

C．it was troublesome to produce such goods in the home

D．the marketplace was more efficient with respect to these processes

Not long ago, a mysterious Christmas card dropped through our mail slot. The envelope was addressed to a man named Raoul, who, I was relatively certain, did not live with us. The envelope wasn't sealed, so I opened it. The inside of the card was blank. Ed, my husband, explained that the card was both from and to the newspaper deliveryman. His name was apparently Raoul, and Raoul wanted a holiday tip. We were meant to put a check inside the card and then drop the envelope in the mail. When your services are rendered at 4 a.m., you can't simply hang around, like a hotel bellboy expecting a tip. You have to be direct.

So I wrote a nice holiday greeting to this man who, in my imagination, fires The New York Times from his bike aimed at our front door, causing more noise with mere newsprint than most people manage with sophisticated black market fireworks.

With a start, I realized that perhaps the reason for the 4 a.m. wake-up noise was not ordinary rudeness but carefully executed spite: I had not tipped Raoul in Christmases past. I honestly hadn't realized I was supposed to. This was the first time he'd used the card tactic. So I got out my checkbook. Somewhere along the line, holiday tipping went from an optional thank-you for a year of services to a Mafia-style. protection racket(收取保护费的黑社会组织).

Several days later, I was bringing our garbage bins back from the curb when I noticed an envelope taped to one of the lids. The outside of the envelope said MICKEY. It had to be another tip request, this time from our garbage collector. Unlike Raoul, Mickey hadn't enclosed his own Christmas card from me. In a way, I appreciated the directness. "I know you don't care how merry my Christmas is, and that's fine", the gesture said. "I want $30, or I'll 'forget' to empty your garbage bin some hot summer day".

I put a check in the envelope and taped it back to the bin. The next morning, Ed noticed that the envelope was gone, though the trash hadn't yet been picked up: "Someone stole Mickey's tip!" Ed was quite certain. He made me call the bank and cancel the check.

But Ed had been wrong. Two weeks later, Mickey left a letter from the bank on our steps. The letter informed Mickey that the check, which he had tried to cash, had been cancelled. The following Tuesday morning, when Ed saw a truck outside, he ran out with his wallet. "Are you Mickey?"

The man looked at him with scorn. "Mickey is the garbageman. I am the recycling". Not only had Ed insulted this man by hinting that he was a garbageman, but he had obviously neglected to tip him. Ed ran back inside for more funds. Then he noticed that the driver of the truck had been watching the whole transaction. He peeled off another twenty and looked around, waving bills in the air. "Anyone else"?

Had we consulted the website of the Emily Post Institute, this embarrassing breach of etiquette(礼节) could have been avoided. Under "trash/recycling collectors" in the institute's Holiday Tipping Guidelines, it says: "$10 to $30 each". You may or may not wish to know that your pet groomer, hairdresser, mailman and UPS guy all expect a holiday tip.

The newspaper deliveryman put a blank card inside the envelope because______.

A．he forgot to write a few words on it

B．he wanted the couple to send it back

C．he used it to ask for a Christmas tip

D．he was afraid of asking for a tip in person

A、3.11 T

B、12.54 T

C、6.27 T

D、7.98 T

A、没有感应电流，没有电动势； no induced current, no electromotive force;

B、没有感应电流，有电动势； there is no induced current and there is an electromotive force;

C、有感应电流，没有电动势； there is an induced current and no electromotive force;

D、有感应电流，有电动势； there is an induced current and an electromotive force;