春秋时期对于各诸侯国来说显得特别重要的是：（）A、手工业B、农业C、军队D、人才

I went to Professor Jayne, who listened to my arguments but remained  unmoved. I decided to try harder,

although I didn' t know what that meant because school had always been easy for me. I read the books more

carefully, but got another 77. Again, I       with Professor Jayne. Again, he listened patiently but wouldn' t

change his  mind. [ ]

A. quarreled

B. reasoned

C. bargained

D. chatted

We can't go to the concert ______ we are quite busy now. [ ]

A. though

B. until

C. because

D. so that

简正振动

相移键控信号的波形为（）

A.正弦波

B.脉冲波

C.方波

D.三角波

我国植物保护总的方针是预防为主，（）。