使用奎尼丁治疗心房纤颤常合用强心苷，因为后者能A．拮抗奎尼丁的血管扩张作用B．拮抗奎尼丁对心脏

Bats (are able) (to guide them) by producing sound waves (too high) for us (to hear).

A．are able

B．to guide them

C．too high

D．to hear

Our guide gave us a detailed ()of this painting but we still do not understand.

A、authority

B、interpretation

C、instruction

D、institution

We demand that the tour guide (tell) ______ us immediately about any change in the schedule.

The teacher told us the fact _______.

A. which the earth moves around the sun

B. that the earth moved around the sun

C. that the sun moves around the earth

D. that the earth moves around the sun

A．conducted

B．controlled

C．taught

D．concluded

Bats (are able) to (guide them) by producing sound waves (too high) for us (to hear).

A．are able

B．guide them

C．too high

D．to hear

The Countess was ______ enough to show us around her home.

A．gracious

B．graceful

C．grateful

D．generous

______ is known to us all, the earth moves around the sun.

A．Because

B．For

C．So

D．As