___ you know the rules of swimming, you will be able to swim well.
| A．Before | B．While | C．Though | D．Once |
The operation room in every hospital has to ______ bacteria of any kind.
| A．keep free from | B．make it free from | C．be made free from | D．be kept free from |
Only ______ a human being.
| A．when is it hungry a lion will attack | B．when it is hungry a lion will attack |
| C．when it is hungry will a lion attack | D．when is it hungry will a lion attack |
The president spoke at the business meeting for nearly an hour without ______ his notes.
| A．bringing up | B．referring to | C．looking for | D．trying on |
— Hi, what did our monitor say just now?
— Every boy and every girl as well as teachers who are to visit Water Cube ______ asked to be at school gate before 6∶30 tomorrow morning.
| A．is | B．were | C．are | D．was |
You’d better spend your time just on the things you find ______.
| A．worth doing them | B．worth being done |
| C．worthy of doing them | D．worthy of being done |