Whether you like it or not，we live in a community_____ on--line chatting is an important part of communication．
| A．which | B．that | C．when | D．where |
When _________ where he had put the book, he kept silent.
| A．ask | B．asking | C．to ask | D．asked |
--- How often do you work out?
--- _________, but usually once a week.
| A．Have no idea. | B．It depends. | C．As usual. | D．Generally speaking. |
Vitamin C helps our bodies make a special chemical, which _______ affects our brains, making us feel happy.
| A．in all | B．in turn | C．in advance | D．in short |
Sex education is a sensitive area for some parents, and thus it should remain _________.
| A．random | B．previous | C．optional | D．vital |
A _______ number of mothers with young children are stopped from undertaking paid work because they lack access to childcare.
| A．considerate | B．critical | C．fundamental | D．substantial |