. It used to be thought _____ the Earth was flat.
| A．as | B．when |
| C．since | D．that |
They chatted ____ coffee about their experience as volunteers during the charity.
| A．over | B．on | C．to | D．with |
A programmer may make mistakes in a wrong analysis of the situation _____ the programme was based.
| A．which | B．of which | C．on which | D．of what |
__________ the directions exactly, you will never get confused.
| A．Follow | B．To follow | C．Following | D．Followed by |
Some people have called ________ the worst period ever for Pop Music.
| A．1990’s | B．the 1990 | C．the 1990’s | D．1990s |
Only after he had spent several nights working on the math problem _______ to wonder whether the problem was wrongly set.
| A．that he began | B．did he begin | C．then he began | D．so that he began |