---What does PM2.5 mean?
--- It’s a professional ______ indicating the condition of air pollution.
| A．number | B．mark | C．term | D．item |
A large sum of money has been raised for the ______ of the poorly-educated children.
| A．interest | B．favour | C．advantage | D．benefit |
—I’m sorry I have failed again in the math exam．
— _________ ? You’ve been working hard at the subject．
| A．How | B．How come | C．Why not | D．When |
—I really don’t know how to thank you enough．
—．
| A．No problem | B．Think nothing of it |
| C．With pleasure | D．Glad to hear that |
On our way to school, suddenly it began to rain, and we hurried to take______under a big tree．
| A．recovery | B．notice | C．advantage | D．shelter |
I can still remember that it is since the 1990’s, _____ we began to use cell phones,_______ the number of mobile users has greatly increased．
| A．while; when | B．when; what | C．before; that | D．when; that |