Advertisers discovered years ago that all of us love to get something for nothing. An advertisement which begins with the magic word free can rarely go wrong. These days, advertisers not only offer free samples, but free cars, free houses, and free trips round the world as well.

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

　　做广告的人们多年前就发现我们大家都喜欢免费得到东西。

　　语言点:句子结构分析:that引导宾语从句，交代discovered的内容。

　　5. An advertisement which begins with the magic word free can rarely go wrong.

　　凡是用“免费”这个神奇的词开头的广告很少会失败的。

　　语言点:句子结构分析:which引导定语从句，修饰advertisement。

　　6. These days, advertisers not only offer free samples, but free cars, free houses, and free trips round the world as well.

　　目前，做广告的人不仅提供免费样品，而且还提供免费汽车，免费住房，免费周游世界。

　　语言点:句子结构分析:not only…but…as well构成并列结构。