单选题 The USA is composed of 50 states, ______ are separated from the others by land or water.
【正确答案】 C
【答案解析】本题考查的是非限制性定语从句。首先不能用that或these,故排除A、D。state州,应用which指代,而非指代人的whom,而且数词two应该放于关系词之前.所以选C。