instruct的主语是editor,在这里,因为前面已有了谓语动词sent,一个句子中若无连接词的话是不能同时出现两个谓语动词的,这里由editor发出的两个动作,前面的动词作谓语,后面的动词要么把它变成带主动的ing形式,或是用and与sent连接在一起,地位和sent一样,变成两个谓语.即原句也可以写成：The editor at once sent the journalist a fax and at the same time instructed him to find out the exact number of the steps .