Since the new speed limits ______，the number of accidents in the area has fallen strikingly．
| A．were introduced | B．introduced |
| C．have been introduced | D．have introduced |
．Ram explained to his mother ________ he would get home late that night because of extra work.
| A．that | B．which |
| C．what | D．whether |
Air pollution is getting more and more serious, so we must take action ________ it is too late.
| A．before | B．after |
| C．until | D．when |
Sarah Brightman, ________ will fly to space in 2015, is the first woman to fly there in the field of music.
| A．who | B．that |
| C．which | D．whose |
The businessman wears a suit and a tie with a beard ________ the season.
| A．whatever | B．wherever |
| C．whenever | D．however |
The course about Chinese food attracts over 100 students per year, ________ up to half are from overseas.
| A．in which | B．for whom |
| C．with which | D．of whom |