下列叙述错误的是（　　）

A．湖水富营养化可以使水草和藻类大量繁殖，从而通过光合作用产生大量氧气

B．废电池应收集起来交有关部门进行安全处理

C．我国西部实行退耕还林的政策是为了改善生态环境

D．盲目引进外来生物很有可能破坏当地的生态平衡

Mary: Helen is a mere washer woman, yet she's now buying a big house.

Carol: Yes. Because she's always saved ________.

A．what little she earns

B．how little she earns

C．for little she earns

D．with little she earns