题目内容：

    Nowadays, we can read almost all “truths” on social media sites. But are they really reliable? Sites such as the micro messaging service Twitter, the social networking site Facebook and the photo-sharing app Instagram might “misrepresent the real world,” according to a study by computer scientists from McGill University and Carnegie Mellon University.

The scientists warn that gathering information about public views and trends from these sites is unwise. There are still large parts of the population who do not take part in social media activities. Also, there's a risk that many social media users are under- represented. Instagram, for example, appeals to younger adults in urban areas while Pinterest is used mainly by females aged 25 to 34. And only 5 percent of Twitter users are over 65 years old, according Io the study.

However, this is not the only issue, according to the scientific team. The design of a website can influence how people behave online, creating what the researchers call “Internet bias.” For example, micro-blogging sites such as Weibo promote “popular” stories. It saves time for some, but it also limits readers' choice of what they see. In the end, many people open those stories and make them more “popular.” But it's not because they choose those stories. Rather, it is because the content is right in front of them.

Besides, it's possible that not everyone on your social networks is real. There might actually be a few fake accounts among them. Fake “bots” pretend to be human and are often included when measuring or predicting human behaviors online.

The findings might be more important than you would think, since many social media studies “are used to inform and justify decisions and investments among the public and in industry and government,” said Derek Ruths, assistant Professor at McGill's School of Computer Science.

If the team is right, you might have to think carefully the next time you say, “It's true, you know; I read it on Weibo.”

1.Why does the author mention Twitter, Facebook and Instagram?

A.Because they are the best social media sites today.

B.Because they are not in favor of the current study.

C.Because the public are sharing truths on these sites.

D.Because information on these sites may not be reliable.

2.How is the passage developed?

A.By giving examples. B.By making comparisons.

C.By dividing into groups. D.By analyzing cause and effect.

3.Which word can best describe the author's attitude toward information on social media sites?

A.Ambiguous. B.Favorable.

C.Disagreeable. D.Cautious

4.What's the author's main purpose in writing the passage?

A.To analyze why information gathered from social media sites may not be trustworthy.

B.To remind readers of things they should watch out for when using social media.

C.To point out the advantages and disadvantages of social media.

D.To recommend popular social networking sites for readers.