I didn't manage to do it ________ you had explained how．

A．until

B．unless

C．when

D．after

When you read the book, you'd better make a mark ________ you have any questions．

A．at which

B．at where

C．the place

D．where

I'll stay here ________ everyone else comes back．

A．even if

B．as though

C．because

D．until

Busy ________ he was, he tried his best to help you．

A．as

B．when

C．since

D．for

________ still half drunk, he made his way home．

A．When

B．Because

C．Though

D．As

It is about ten years ________ I met you last．

A．since

B．for

C．when

D．as

I won't call you, ________ something unexpected happens．

A．unless

B．whether

C．because

D．while

He was told that it would be at least three more months ________ he could recover and return to work．

A．when

B．before

C．since

D．that

Many of them turned a deaf ear to his advice, ________ they knew it to be valuable．

A．as if

B．now that

C．even though

D．so that

Leave your key with a neighbor ________ you lock yourself out one day．

A．ever since

B．even if

C．soon after

D．in ease