3x2+2x-3(x2-13x)
=3x2+2x-3x2+x
=3x,
当x=-13时,原式=3×(-13)=-1.
—Is this your pencil?
—Yes, ______. [ ]
A. it's
B. it is
C. its
D. is it
现代化加热炉的标志是,用最低的(),加热出优质的钢坯。