—________ will you ask for help when you get into trouble?
—My parents, I think.
A:Who
B:What
C:Where
已知(2x﹣21)(3x﹣7)﹣(3x﹣7)(x﹣13)可分解因式为(3x+a)(x+b),其中a,b均为整数,则a+3b等于多少?
关于变异的说法,不正确的是( )