We must try our best to         the river being polluted any more.
#101113
A
separate
B
keep
C
prevent
D
guard
推荐题目
— I _______ the dishes for over a week. It’s your turn.— I ______ you would say something like that.
#99838
A
have washed; have known
B
have been washing; knew
C
have washed; know
D
have been washing; know
Selecting a mobile phone for personal use is no easy task because technology ____ so rapidly.
#100268
A
will change
B
has changed
C
will have changed
D
is changing
The vegetables didn’t taste very good.They____too long. 
#104667
A
had been cooked
B
were cooked
C
had cooked
D
cooked