1.2x与(x-5)的3倍的差是_______.
2.一个多项式减去a2-b2等于a2+b2+c2,则原多项式是______________.
3.若-3x2y+ax2y=-6x2y,则a=________.
4.把3+[3a-2(a-1)]化简得________.
5.已知a2-ab=2,3a2-3ab+2=________,5-2a2+2ab=________,
二、选择题
6.下列去括号中,正确的是 ( )
A.a2-(2a-1)=a2-2a-1 B.a2+(-2a-3)=a2-2a+3
C.3a-[5b-(2c-1)]=3a-5b+2c-1 D.-(a+b)+(c-d)=-a-b-c+d
7.化简2-[2(x+3y)-3(x-2y)]的结果是 ( )
A.x+2 B.x-12y+2 C.-5x+12y+2 D.2-5x