单选题 Dump sewage into oceans and rivers is a serious form of pollution.
A. Having dumped sewage B. Being dumped sewage
C. Dumped sewage D. Dumping sewage

【正确答案】 D
【答案解析】[解析] 本题考查动名词作主语。句意为：把污水排入海洋和河流是一种严重的污染形式。句中已经有谓语了，所以只能用动名词作主语。所以，答案是D。