一Is your sister a worker or a doctor?
— ________．
| A．She is twenty． | B．No，she isn’t |
| C．She is a doctor | D．She likes her job |
There are several chemical factories ______ waste water into the river.
A. pours B. pour C. pouring
Jim has been to the Great Wall before, ______ he?
A. has B. does C. hasn’t
The city has improved a lot _________ I came here a few years ago.
A. sinceB. forC. when
The weather in summer here is cooler than ______ in Beijing.
A. this B. that C. it
In our class, about ______ of the students are girls.
A. three fifths B. third fifth C. third fifths