According to paragraph 2, what do the scientists d...

Câu hỏi: According to paragraph 2, what do the scientists discover in their  study?

A. Spending too much time on Facebook may increase levels of pressure and heart  disease.

B. Students often suffer from stress when they are working with something related to mathematics.

C. Facebook can make its users more optimistic and  aroused.

D. The success of Facebook may motivate the development of other social networks.