---Is it Pro. King that will give the lecture on radiation?--- I can't __ I know it for sure.
Persist to the end , _______ you are the only one left.
He always talks _______ he had been to outer space.
You’d better come back earlier _______ it is getting colder.
He was walking along the sands _______ he saw a big foot-print in the sand . A. whileB. whenD. asD. after
_______ he was sleeping , they stole his clothes.