the young man has been a doctor _______.A.five years agoB.since five years befoeC.for five yearsD.since five years ago B和D有什么根本上的区别吗?C是 for five year .

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theyoungmanhasbeenadoctor_______.A.fiveyearsagoB.sincefiveyearsbefoeC.forfiveyearsD.sincefiveyearsag

the young man has been a doctor _______.A.five years agoB.since five years befoeC.for five yearsD.since five years ago B和D有什么根本上的区别吗?C是 for five year .
the young man has been a doctor _______.
A.five years ago
B.since five years befoe
C.for five years
D.since five years ago
B和D有什么根本上的区别吗?
C是 for five year .

the young man has been a doctor _______.A.five years agoB.since five years befoeC.for five yearsD.since five years ago B和D有什么根本上的区别吗?C是 for five year .
C B是错的 D表示的是自从5年前.这里是指已经5年了

C B和D都是有关since后加句子和现在完成时的连用~~since后一般跟句子,用过去时,多与现在完成时连用,而for后长跟时间段