(2013·重庆模拟)—When did your brother begin to show his interest in medicine? —It was a Saturday　　　he noticed his classmate experimenting on a frog in the lab.

book do you think is the most useful to mystudies—________, as long as you read it. In fact, they areout of date.

They finally arrived ________ the bus stop ________ a cold winter evening

____ in a theater wearing 3D glasses, you feelas though you are caught up in the story which is showing around you

the first person you can think of torely on, for he is always willing to ________ whoever is in trouble