______ 2000，this company has seen much new development．It has become one of the biggest companies in the country．（ ）
| A． |
For |
B． |
In |
C． |
By |
D． |
Since |
The water dark and dirty．It's no longer safe to drink．（ ）
| A． |
became |
B． |
has become |
| C． |
will become |
D． |
was becoming |
Last night，the shop was closed she didn't buy any chocolate．（ ）
| A． |
so |
B． |
if |
C． |
or |
D． |
when |
Some old people need a _______ because they feel lonely．（ ）
| A． |
gift |
B． |
stick |
C． |
pet |
D． |
watch |
By the time the teacher came, we ______ cleaning the classroom．（ ）
| A． |
finished |
| B． |
have finished |
| C． |
had finished |
_____ walk on the grass．（ ）
| A． |
Doesn't |
B． |
Don't |
C． |
Not |