英语选择题~~~!1.Birds are often heard _____ in the morning.A.to s

英语选择题~~~!
1.Birds are often heard _____ in the morning.
A.to sing B.sing C.sang D.sung
答案是A,为什么?
2.I don't think he will come,_____?
A.do I B.don't I C.won't I D.will he
答案是D,为什么不能选A?
3.Computers can work out the maths problems ______ than we do.
A.even quicker B.much quickly C.far more quickly D.more quicker
答案是C,为什么?