在下列运算中,正确的是 [ ]
A .a2÷a=a2
B .(-a )6÷a2= (-a )3= -a3
C .a2÷a2=a2 -2=0
D .(-a )3÷a2= -a
答案:D
口外正畸力的一般力值是()
A.340~450g
B.100~150g
C.200~250g
D.300g
E.800~1100g
After class we try to talk both Chinese and English.[ ]
A. in
B. with
C. on
D. by