—What does PM 2.5 mean?
—It's a professional ________ indicating the condition of air pollution.
| A．term | B．item | C．number | D．mark |
A teacher's ___ to education is worth great respect of the whole society because it brings benefits to the development of society．
| A．devotion | B．principle | C．identity | D．guidance |
—What do you think of the American singer Lady Gaga?
—Too crazy, but if she ___ come to China to hold concerts, I would buy tickets for her live show．
| A．would | B．could | C．should | D．might |
___ more and more people may refer to the Internet for the latest news, it is unlikely that the newspaper will disappear．
| A．When | B．Because | C．Since | D．While |
—I'm sorry; I shouldn't have been so rude to you．
—You ___ something not very nice to me, but that's OK．
| A．have said | B．had said | C．were saying | D．did say |
—Can you describe ___ it happened?
—Yes, I was riding on my bike ___ a car knocked me down from behind．
| A．when; as | B．how; as | C．how; when | D．how; while |