对于鲜活食品，应在其成熟之前采收并采取控制储藏条件的办法，来调节其后熟过程，以达到延长储藏期，均衡上市时间、先进先出的目的。

The factory produces half a million pairs of shoes every year, _________ are sold abroad.

A．80% of them

B．80% of that

C．80% of the shoes

D．80% of which