________ more energy to my study instead of being crazy about Internet games, I would be sitting in a comfortable office now.( )
A:If I devoted
B:Had I devoted
C:Would I be devoted
D:Should I be devoted
(2015•临沂)定义:给定关于x的函数y,对于该函数图象上任意两点(x1,y1),(x2,y2),当x1<x2时,都有y1<y2,称该函数为增函数,根据以上定义,可以判断下面所给的函数中,是增函数的有 ____ (填上所有正确答案的序号)
①y=2x;②y=﹣x+1;③y=x2(x>0);④y=﹣1x.