How ___I help them to understand when they won’t listen to me?
| A．can | B．would | C．may | D．must |
In summer, food will go bad if________in room temperature.
| A．leaving | B．left | C．being left | D．having left |
QQ, you can chat with your friends, makes communication easy.
| A．why | B．which | C．that | D．where |
Mike must be angry with me, for he walked me without even saying hello.
| A．past | B．on | C．at | D．over |
_____ you don’t lose heart, I’m sure you can pass the coming examination.
| A．Unless | B．As long as | C．If not | D．Although |