下列以十字花科植物为食的昆虫是( )
A.棉铃虫
B.蝗虫
C.菜粉蝶
D.七星瓢虫
答案:C
—Can I have a day off tomorrow, Mr. Johnson?
—__________. I can manage without you.
A.Forget it
B.I’m afraid not
C.It depends
D.Of course
试述东风4型内燃机车制动缸的构造和作用?