语法与词汇

Even at low levels, ________ .

A、 the nervous system has produced detrimental effects by lead
B、 lead‟s detrimental effects are producing the nervous system
C、 lead produces detrimental effects on the nervous system
D、 the detrimental effects produced by lead on the nervous system

【正确答案】 C

【答案解析】

句意：即使少量的铅也对神经系统产生有害影响。
从句的逻辑主语是lead，但是省略了主语lead和谓语is。