請問instructing him...在句子中干什么成分？為何不是用to instruct him?The editor at once sent the journalist a fax instructing him to find out the exact number of steps....

The editor at once sent the journalist a fax instructing him to find out the exact number of steps.

目前分詞 instructing...，是隨著狀語，也暗示肯定的目的性。表示在發傳真的同時，“指示”這個動作也在發生，也就是說，兩個動作是同時發生的。大家了解，不定式表示以后，目的性非常強。本句若用不定式 toinstruct...，“為了指示...才發電報”，不符合句意。

目前分詞作隨著狀語，也總是帶有目的性。比如：

She waited impatiently, hoping he could come earlier.

她不耐煩地等待著，期望他能早點來。

The professor put a finger in his mouth, tasted it and smiled,looking rather pleased.

教授把一個手指放進嘴里，嘗了嘗，笑了，看著非常高興。

The secretary worked late into night, preparing a report for the manager.

秘書為了給經理籌備一個報告而工作到深夜。