It is difficult to measure the quantity of paper used as a result of use of Internet-connected computers(主句:
形式主语it,真正主语是to measure...), although just about anyone who works in an office can tell you that when e-mail is introduced, the printers start working overtime(
让步状语从句).That is, (the growing demand for paper in recent years主语) is(
系动词) (largely due to the increased use of the Internet
表语).
虽然几乎每位在办公室工作的人都会告诉你,当引进
电子邮件后,打印机就开始超时工作,但是由于因特网的使用,很难算出所使用的纸张的数量。也就是说近年来人们对于纸张的日益需求主要是由于因特网使用量的增加。