A:a=2, b=3
B:a=3, b=2
C:a=-3, b=-2
D:a=- 2, b=-3
设m≠n,x=m4﹣m3•n,y=n3•m﹣n4,比较x与y的大小.
I often have ______ homework to do.
吃桑叶的“蚕宝宝”(如图),在蚕发育过程中所处的阶段是( )