单项选择题
A．Seasonal differences in what mothers ate during pregnancy. B．Infection occurring at different times of the year. C．Its family background. D．Both A and B.
A．The problem may have been a very complicated one. B．No one can solve this problem. C．The man thinks that the problem is quite easy for Linda. D．The man thinks that he can solve the problem himself.
A．University. B．Community College. C．Middle school. D．Primary school.