It was a while before Tom could appreciate the joke .while在句子中的作用,句子成分各有哪些,怎么翻译?

it is over 30 years （）shengzhen was established as a special zone……befor since那个为什么 1i will let you know as snow as he -________A arrives B is going to arrive C will arrive D is arriving 2paul was doing his homework ______ there was a knock on the door .who could it be A befor B while C when D after (请给原因?） Don't worry I will tell him ___ he comes back A befor Bas soon as C while D befor Once,I let a ture love,slip away befor my eyes,Once,I let a ture love,slip away befor my eyes,only to find myself regretting when it was too late While it was buying a sounvenir,I called the police是什么意思?while是什么意思? The English book was so interesting that she had read it for 3hours_she realized.A.when B.until C.befor D.after为什么选C I was a bit nervous befor I arriver here,but there was no reason ____ across the railway ,a train hit it.A While walkingB Walking slowlyC As it was walkingD While the sheep was walking It was a cold evening.It s while an old man was walking in the street.原文, -- When _____ you _____ your homework?--I had finished it befor he_____ back.A.have;finished;came B.have;finished;was comingC.did;finish;came C.did finish;was coming not to know what happened befor one was born is always to be a chilld是什么 _____ my mother is cooking , we play games and watch televison A While B Befor C After D Until It was yesterday_____he told me the news.A.when B.while C.that D.which He cut （ ）while he was shaving A,him B,his C,himself D,it _______we got home it was very late.A.When B.While C.Because D.As while she was playing with her golden ball,it fell into a pond找动词 Nearly a week passed before the girl was able to explain what happened to her.为什么用befor?为什么用befor,不用after? it worried her a bit___her hair was turning grey.A.while B.that C.it D.for