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下列计算正确的是( )
A. B.
C. D.6m―m=6
下列计算正确的是
A.(a-2b)(3a+b)=3a2-5ab-2b2
B.(2x+1)(2x-1)=4x2-x-1
C.(x-y)(x+y)=x2-2xy+y2
D.(m+2)(3m+6)=3m2+6m+12