We shouldn’t do that dangerous experiment ________ the teacher is with as．

A．if not

B．if

C．unless

D．as long as

I was walking along the river ________ I heard a cry for help．

A．while

B．since

C．when

D．as

He can’t have gone out, ________ the light is still on．

A．because

B．since

C．as

D．for

________ the day went on ,the weather got worse．

A．With

B．Since

C．As

D．While

________ the baby fell asleep ________ the room．

A．After；did the mother leave

B．Not until；did the mother leave

C．Not until；the mother left

D．Soon after；the mother had left

I’ll start early,________ it may be dark．

A．however

B．whether

C．if

D．though

________ that none of us could follow him．

A．He spoke very fast

B．So fast he spoke

C．Too fast he spoke

D．So fast did he speak

You’d better do ________ you are required．

A．like

B．which

C．that

D．as

________ we have come,let’s stay and enjoy it．

A．For

B．As

C．Because

D．Since

________ many times，but he still couldn’t understand it．

A．Having been told

B．Though had been told

C．He was told

D．Having told