胆固醇结石大部分位于胆囊内。（）
参考答案：对
There are so many foggy days these days. We all wonder .
A. how is the air polluted
B. why the air is polluted seriously
C. what are the real reasons
导致人类艾滋病的病原是（）
A.HTLV
B.CMV
C.HBV
D.HIV
E.HPV
