英语-虚拟语气1 He was very busy yesterday; otherwise,he ___to the

英语-虚拟语气
1 He was very busy yesterday; otherwise,he ___to the meeting
A would come B came C would have come D will come
2.The librarian insisted that John ___ no more books from the library before he returned all the books he had borrowed.
这里的insist是“坚持”还是“坚持做某事”为什么用takes
3.If only the alarm clock __then!
A had rung B ring C would set off Dshall ser off
第3句话不明白意思
希望明白这些句子的人能给我详细的讲解一下