【题目】Mary really hard on his book and thinks he'll have finished it by Friday.
A.worked
B.has been working
C.had worked
D.has worked

【答案】B
【解析】句意：Marty一直努力写书，我想他到周五为止将已经完成了。用现在完成进行时表示从过去到现在一直进行的动作。所以选B。