下列运算正确的是 ( ) A.23=6 B.(-y2) 3=y6 C.(m2n) 3=m5n3 D.-2x2+5x2=3x2 答案:D 【解析】 试题分析:根据同底数幂相乘,底数不变,指数相加,可知23=5,故不正确; 根据幂的乘方,可知(-y2) 3=-y6,故不正确; 根据积的乘方,等于各个因式分别乘方,可知(m2n) 3=m6n3,故不正确; 根据合并同类项法则,可知-2x2+5x2=3x2,故正确. 故选D13、--Look! How fast he is running!
--Hard to _________ his legs were
once broken.
A.know
B.realize
C.imagine
D find