单选题 How many people A realize that agriculture is a B source of raw C materials for clothing and D to shelter ?
【正确答案】 D
【答案解析】解析:to shelter一sheltering。句意:有多少人意识到农业是制衣和遮盖物的原料来源?and连接两个并列的名词成分,clothing为动名词形式,而to shelter为动词不定式形式,故答案为D。