—— __________ hard-working girl! Who is she? ——Tina. She tried to _________ many problems to learn Chinese.
A:How; get on
B:How a; get off
C:What a; get over
D:What; get out
已知函数f(x)=(cos2xcosx+sin2xsinx)sinx,x∈R,则f(x)是( )