To give you a general idea of the various cotton piece goods now available for export, we ______ a brochure and a sample-cutting booklet.

A．enclose
B．enclose you
C．enclose to you
D．enclose for you

代数式(2x³－3x²y－2xy²)－(x³－2xy²+y³)+(-x³+3x²y－y³)的值，其中x="0.5," y= -1时，甲同学把x=0.5错抄成x= -0.5，但他计算的结果是正确的.试说明理由，并求出这个结果.