1,John,look at the time,_______ you play the piano at such a late hour?

1,John,look at the time,_______ you play the piano at such a late hour?
A must B can C may D need
答案是选A,答案说在询问对方意愿时应用must,但need为什么不行呢,need有‘必须’之意,也可以用在疑问句中,这句话不可以翻译成‘你必须在这么晚的时间弹琴吗?’吗,如果这样翻译那need不是可以吗?
2,The teacher _____ have thought Jhnson was worth it or she would not have wasted time on him,I support.
A should B can C would D must
or不是连词吗,起并列关系吗,or后有would,那前空对应不就要填would吗?但答案是must,为什么?另外这个句子如何翻译啊?看不太懂!
3,If it were not for the fact that she ______ sing,I would invite her to the party.
A could't B should't C can't D might not
但从were可以看出是过去时态,答案C为什么可以呢?can't可不是过去式啊!为什么呢?