______ a good insulator(绝缘体) , rubber is often used in cables.
Choosing the right dictionary depends on ______ you want to use it for.
Having checked the doors were closed , and _________ all the lights were off, the boy opened the door to his bedroom.
It is none of your business _____ other people think about you. Believe yourself.
Why not try your luck downtown, Bob? That’s ______ the best jobs are.
You can only be sure of_________ you have at present; you cannot be sure of something _____ you might get in the future.