I had wanted to help you last night but I couldn’t spare any time, for I ______ a composition which I have to hand in this morning.

A．wrote

B．was writing

C．had written

D．have written

猪繁殖与呼吸综合征的主要临诊特征是（）

A.母猪发生流产

B.仔猪发生呼吸道症状

C.哺乳仔猪脱水，呼吸困难和高死亡率

D.以上都是

E.以上都不是