In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.

Let me give you an example: Article: Homework can put you in a badmood , and that might actually be a good thing. Researchers from the University of Plymouth in England doubted whether mood might affect the way kids learn. To find out the answer, they did two experiments with children. The first experiment tested 30 kids. Someshapes were hidden inside a different, larger picture. The kids had to find the small shapes while sitting in a room with either cheerful or sad music playing in the background. To test their mood, the scientists asked the kids to point to one of five faces, from happy to sad. Children who listened to cheerful music tended to point to the smiley faces while the others pointed to the unhappy ones. The researchers found that sad kids took at least a second less to find the small shapes. They also found an average of three or four more shapes. In the second experiment, 61 children watched one of two scenes from a film. One scene was happy, and the other was sad. Just like in the first experiment, kids who saw the sad scene acted better compared to the others. The researchers guessed that feeling down makes people more likely to focus on a problem or difficult situation. Not all scientists agree with them, however. Other studies argued that maybe, that cheerful music in the first experiment distracted kids from finding shapes. While scientists work on finding out the answers, it still might be wise to choose when to do your tasks according to your mood. After eating a delicious ice cream, for example, write an essay.
Answer: whether mood affects their learning ability
The answer to this example can be: Researchers did experiments on kids in order to find out _ .
Here is why: It is clearly mentioned in the article that to the check effect of mood on children is the main purpose of the experiment.

OK. solve this:
Article: Blogging may have psychological benefits for teens suffering from social anxiety, improving their self-esteem and helping them relate better to their friends, according to new research published by the American Psychological Association. "Research has shown that writing a personal diary and other forms of expressive writing are a great way to release emotional distress and just feel better," said the study's lead author, Meyran Boniel-Nissim, PhD, of the University of Haifa, Israel. "Teens are online anyway, so blogging enables free expression and easy communication with others." Blogging has a stronger positive effect on troubled students' well-being than merely expressing their social anxieties and concerns in a private diary, according to the article published online in the APA journal Psychological Services(r). Opening the blog up to comments from the online community intensified those effects. The researchers randomly surveyed high school students in Israel, who had agreed to fill out a questionnaire about their feelings on the quality of their social relationships. A total of 161 students -- 124 girls and 37 boys, with an average age of 15 -- were selected because their scores on the survey showed they all had some level of social anxiety or distress. All the teens reported difficulty making friends or relating to the friends they had. The researchers assessed the teens' self-esteem, everyday social activities and behaviors before, immediately after two months and after the 10-week experiment. Four groups of students were assigned to blog. Two of those groups were told to focus their posts on their social problems, with one group opening the posts to comments; the other two groups could write about whatever they wanted and, again, one group opened the blog up to comments. The number and content of comments were not evaluated for this experiment. The students could respond to comments but that was not required. Two more groups acted as _ -- either writing a private diary about their social problems or doing nothing. Participants in the writing and blogging groups were told to post messages at least twice a week for 10 weeks. Four experts, who held master's or doctoral degrees in counseling and psychology, assessed the bloggers' social and emotional condition via their blog posts. Students were assessed as having a poor social and emotional state if they wrote extensively about personal problems or bad relationships or showed evidence of low self-esteem, for example. Self-esteem, social anxiety, emotional distress and the number of positive social behaviors improved significantly for the bloggers when compared to the teens who did nothing and those who wrote private diaries. Bloggers who were instructed to write specifically about their difficulties and whose blogs were open to comments improved the most. All of these results were consistent at the two month follow-up. The authors conceded that the skewed sex ratio was a limitation to the study. However, the researchers analyzed the results separately by gender and found that boys and girls reacted similarly to the interventions and there were no major differences. They said future research should attempt to control the subjects for sex.
Answer: their willingness to fill out a questionnaire
Answer:
The selection of students for the experiment was largely based on _ .