41. research shows that 30% of all patients in a psyco--- hospital admits depression clinic,while only 15%of all patients have antibody of a kind of virus, since only when infected by the virus, an person will obtain the antibody.thus the scientists conclude that it is the virus that cause the depression. ask support i chooose less than 2% of people in general have the antibody.
这题不懂啥意思?
42. a kind of birds return very early this spring, because the spring came early this year.but because of the lack of insect, the birds have less food, however, the birds thrive. ask the explanation. i choose the number of predators of the birds have been influenced too.