Question

Mark Twain worked for several years as a pilot on a steamboat, taking passengers up and
down the Mississippi, the great river ___flows from the north of the US near the Canadianborder.

A．as

B．what

C．which

D．who

Answer 1

C

试题分析：考查定语从句。Which指代先行词river在定语从句中做主语；故C正确。
点评：定语从句的关键在于分析句子成分，如果句子很完整就使用冠词副词；如果句子中缺少主语，宾语，表语或者定语则使用关系代词。