A is the right answer,please tell me why.

问题描述:

A is the right answer,please tell me why.
The two friends_____on the internet for three hours,and they would go on till the next morning.
A had been chatting B had chatted C were chatting D has been chatting
A 是对的,为什么不选其他的啊,原因和翻译中文
the terrorists might have planed a bomb on a plane in Athens,set to _____when it arrived in new york.
A get off B carry off C go off D come off
当然我知道C是正确答案,但是分别的意思和在句中的意思,全部翻译
the old man was sitting by riverside with his eyes___on the far-away ship.
A fixed B being fixed C fixing D fix
选择 A,告诉我原因和解释为什么不选其他的

B 是已经谈完了,而他们实际上还在聊.
C 是正在聊,但没有“已经”谈了3个小时的意思.
D 现在完成时,与整个句子的时态不符.应该是过去完成时才对.
整句话意思是:
这两位老友已经在网上聊了三个小时了,而且他们会继续聊到次日清晨.
另一题已经在其他板块回答了,但审查还没通过.