第1个回答 2012-09-29
they should have arrived here one hour ago.
用虚拟语气表示实际没有到达
第2个回答 2012-09-28
They should have been here an hour ago. should have done 表示本来应该做某事而实际未作。
第3个回答 2012-09-28
They were supposed to reach here an hour ago.
第4个回答 2012-09-29
They should have arrived an hour ago.