The energy from the sun and wind is very cheap and will never ________．（ ）
| A． |
run out |
B． |
cut out |
C． |
come out |
D． |
give out |
This weekend our class will go to a mountain near our city_________ trees．（ ）
| A． |
plant |
B． |
planted |
C． |
to plant |
D． |
planting |
Hi，madam．Can I take the story books out？
No，my boy．They _______be taken out of the reading﹣room．It's a rule．（ ）
| A． |
mustn't |
B． |
needn't |
C． |
couldn't |
D． |
wouldn't |
Mom，could I watch the game show now？
Sorry，you can't watch it ________you clean your room．（ ）
| A． |
when |
B． |
if |
C． |
after |
D． |
until |
Look，the light is still on in Helen's office．
Maybe she_________ her work yet．（ ）
| A． |
doesn't finish |
B． |
won't finish |
| C． |
hasn't finished |
D． |
didn't finish |
If more people give up driving cars，the air will get much in a few years．（ ）
| A． |
clean |
B． |
cleaner |
| C． |
the cleaner |
D． |
the cleanest |