harvesting has begun earlier than usual.it____yet.

问题描述:

harvesting has begun earlier than usual.it____yet.
1 hasn't finished 2 didn't finish 3 hadn't finished 4 isn't finishing
请问选择哪一个,及分别说出每个为什么对与错

答案是 1
1 强调到目前为止.has begun是现在完成时,所以2是不对的,2指的是过去某一个时间.4没有这个表达法.3讲的是过去的过去,而语境所给的是现在完成时,所以也不能用.
2