下列运算正确的是（　　）

A．x²•x³=x⁶

B．x²+x²=2x⁴

C．（-2x）²=4x²

D．（-2x）²•（-3x）³=6x⁵

It’ s said that they will______ building a big mall here.

A．set out

B．set about

C．set aside

D．set up