A:①
B:①②
C:①②③
D:①②③④
(1) ( cosxx )′= −sinxx2
(2) (x2+x+1)ex′=(2x+1)ex
(3) ( 2xx2+1 )′= 2−2x2(x2+1)2
(4) (e3x+1)′=3e3x+1.