.—Must I turn off the gas after cooking ? --Of course . You can never be ___ careful with that.
| A．enough | B．too | C．so | D．very |
While we are developing agriculture and industry, we must prevent the earth ______.
| A．from polluting | B．polluted |
| C．polluting | D．being polluted |
When _______ help, one often says “Thank you.” or “It is kind of you “
| A．offering | B．to offer | C．to be offered | D．offered |
Frank insisted that he was not asleep______ I had great difficulty in waking him up.
| A．whether | B．although | C．for | D．so |
_______seems to have been a strong competition in China for school leavers to enter college or university.
| A．It | B．There | C．Here | D．That |
It is these poisonous products ______can cause the symptom of the flu, such as the headache and aching muscles.
| A．who | B．that | C．how | D．what |