4,  advertisers have made a close study of human nature and have classified all our little weaknesses.新概念第三册

  make a close (careful ) study:对什么做了仔细的研究

Advertisers make every effort in order to sell their products

5, Advertisers discovered years ago that all of us love to get something for nothing.

 get something for nothing ( free ): 免费得到…….

6,  They devise hundreds of competitions which will enable us to win huge sums of money.

 enable sb. to do: 使某人能够做某事

Eg.: Hard work will enable you to pass the examinaiton, otherwise, no way.