.______ the beginning of the 19th century did scientists know that all matter is made up of atoms.

A. At          B. By            C. Up to         D. Not until

— Were you worried about him last night?

　　　　— Yes. It was ________.

　　A. until he returned that I went to bed

　　B. until be returned that l slept well

　　C. not until he returned that I went to bed

　　D. not until did he return that I went to sleep

. ---Did he hear of the news that his son sacrificed in the war?

   ---No. It was   he received the call from the army   he knew it.

A. until, that                   B. not until, when           C. until, when                  D. not until, that

It was ____ the old worker came that we ____ the  experiment.

    A. until; didn’t begin              B. not until; began

    C. until; began                     D. not until; didn’t begin

It was ______ his office.

A. not until the rain stopped did he leave

B. not until did the rain stop that he left

C. not until the rain stopped when he left

D. not until the rain stopped that he left