请根据上下文内容，将文中划线部分译成汉语或者英语。
Nowadays, ads are playing an important part in our lives. 无论我们去哪里都能发现他们。I did some research on advertisements。我有些重要的信息同大家分享。
One of the aims of ads is to persuade people to buy products or service or believe in an idea. So in this way, maybe the contents of some ads are not true and likely to use words of tricks for us to fall for them. So, with so many ads around, we should be smart about what to buy.
Not all ads play tricks on us though. The ads called public service advertisements may not be the same. They are meant to serve us and teach us and help us to lead better lives. PSAs are often placed in public places for free. They deal with widespread social concerns, which often benefit the public. Such as, ‘Yes to life, no to drugs’ and ‘Knowledge changes life.’  All of these ads are helpful, and you can learn a lot by following the advice they give.