题目

 He was in a hurry the other day. Otherwise he _____ you repair the machine.  A. would help   B. should help   C. would be helping  D. would have helped 答案：D4．已知：如图，⊙O的半径是5cm，PA、PB切⊙O于点A、B两点，∠PAB=60°．求AB的长．