老龄化问题主要是（）的研究课题。
A.家庭社会学
B.家庭理财
C.婚姻家庭心理学
D.家庭教育
参考答案：A
Alan his father and both of them are friendly.
A．looks after
B．takes after
C．feels like
D．is after
脊椎动物学
