We must not touch this switch under any ______.
| A．situation | B．atmosphere |
| C．circumstances | D．civilization |
There are 40 students in our class，who come from a ________of backgrounds.
| A．variety | B．mixture | C．extension | D．combination |
—Hi，Peter. Long time no see.
—Oh，it’s you，Jack. I’m sorry I didn’t ________ you at first.
| A．know | B．recognize | C．remember | D．realize |
People are encouraged to speak openly，but careless words are ________to hurt others’ feelings.
| A．possible | B．probable | C．likely | D．sure |
Our bodies are strengthened by taking exercise. ________，our minds are developed by learning.
| A．Probably | B．Likely | C．Similarly | D．Generally |
Smoking is one of the ________causes of cancer，killing millions of people each year.
| A．major | B．similar | C．commercial | D．chemical |