题目

When he was alive, the old scientist used to say that knowledge ＿＿from practice and he gained his experience by doing a lot of practical work. A. was coming    B. had come    C. comes      D. would come 答案：C 解析: 宾语从句表示的是客观事实。4．下列过程不会造成空气污染的是（　　）A．煤燃烧生成二氧化碳、二氧化硫等B．石油化工厂排放的废气C．氢气燃烧生成水D．汽车排出的二氧化氮等尾气