1.Tom ____ the accident ____ ____ ____ ____ (亲眼目睹）.He could tell you in detail.
2.This ____ in a short time.We still have something more important to do.
A.can't be done B.can done C.mustn't be done D.have been finished .
3.Put the stone ____ ____ ____ ____（相隔）20 meters from the door.
4.____ ____ （三分之一）of the leaves of the tree have turned yellow.
5.Something expensive in her house was stolen.The policemen ____ ____ ____(search for)the thief.
最好能解释下 原因