What’s the matter with you ?—Oh, I’m not feeling well in the stomach . I ______so much fried fish just now .

The theory he sticks to ______ to be of no use in our studies.

The students asked Mr. Wang ______ them some advice on reading.

Experiments of this kind ___in both the U.S and Europe well before the Second World War

Rubbish in space has caused collisions, which would ______ produce more rubbish that threatens astronauts and satellites.