it, that還是which

請看這道題：

Jim is always really rude, ______ is why people tend to avoid him.

A. that            B. it             C. this            D. which

此題容易誤選 A，因為 that’s why … 是一個常用表達，同學們極易受此影響而選錯，當然若此句的空格前有連詞 and 或其前的逗號改為分號，則完全可選that（分別構成并列句和兩個獨立的簡單句）。此題的最佳答案是 D，句子后半部分為一個非限制性定語從句，which 指 He is always really rude. 另外請比較以下兩題（注意連詞的有無）：

(1) He had a lot of friends, none of ______ could lend him any money.

A. whom         B. them           C. which          D. who

(2) He had a lot of friends, but none of ______ could lend him any money.

A. whom         B. them           C. which          D. who

第(1)題選A，none of whom could … 為非限制性定語從句；第(2)題選B，由于句中有并列連詞 but，整個句子為并列句。