When products made in factories _____, they are thrown away as garbage.

A．come to an end

B．are put to use

C．are used up

D．wear out

（）就是把同类事物两种以上的表现形式归并为一种，或限定在一个内的标准化形式。

A.简化

B.统一

C.协调

D.优化