题目下列去括号变形正确的是（ ）A.a+(b−c)=ab−ca+\left(b-c\right)=ab-ca+(b−c)=ab−cB.3a−(b+c−d)=3a−b+c−d3a-\left(b+c-d\right)=3a-b+c-d3a−(b+c−d)=3a−b+c−dC.m+4(p+q)=m+4p+qm+4\left(p+q\right)=m+4p+qm+4(p+q)=m+4p+qD.12(−x+4y−6z)=−12x+2y−3z\frac{1}{2}\left(-x+4y-6z\right)=-\frac{1}{2}x+2y-3z21(−x+4y−6z)=−21x+2y−3z知识点：去括号与添括号章节：第4章 整式的加减 / 4.2 整式的加法和减法
