一、基本方法

　　如果空格前后为介词结构，回原文找介词结构。

　　二、出题形式

　　介词在原文可能是题目中的原词，也可能是题目中介词的同义结构。

　　例一（原文介词为题目中的原词），

　　……This was followed by a lull, but in early May the top of the mountain rose by ……People were evacuated from around the mountain. Finally, on May 18th at……, Mount St. Helens exploded.（雅思样题）

　　原文：Then, in early May, the northern flank of the mountain bulged, and the summit rose by 500 feet.

　　……On May 18, at 8.32 in the morning, Mount St. Helens blew its top, literally.

　　对于第一空，根据early May定位原文，再根据介词by确定答案之一为500 feet；对于第二空，根据May 18定位原文，再根据介词at确定答案之一为8.32.

　　例二（原文介词为题目中介词的同义结构）

　　According to his biographer, James Boswell, Johnson's principal achievement was to bring……to the English language. As a reward for his hard work, he was granted a pension by the king. （剑5 Test 1 Reading Passage 1）

　　原文：It is the cornerstone of Standard English, an achievement which, in James Boswell's words, 'conferred stability on the language of his country'.

　　根据James Boswell、achievement等定位原文，再根据介词结构bring……to找介词结构：conferred stability on……，由于两个介词结构属于同义结构，那么题目中介词to之前的答案应为原文介词on之前的部分：stability.