Read the following passage and mark the letter A, B, C, or D to indicate the correct answer that best fits each of the numbered blanks.

People who use the Internet too much may have mental health problems. They may have problems if they cannot get online regularly. A survey from a Canadian university looked at the Internet (21) __________ of 254 students and their mental health. Researchers said 107 students were addicted or had problems like depression or anxiety (22) __________ their Internet use. We know little about the dangers of Internet addiction and need to do more research.
A researcher explained (23) __________ problems there are. He said: "We found that students addicted to the Internet had significantly more trouble dealing with their day-to-day activities, (24) __________ life at home, at work or at school." He added: "People with Internet addiction also had significantly higher amounts of depression, and problems with time management." We also need to (25) __________ if mental health problems cause Internet addiction.