50kg重的健康人，其血量约为（）
A.3L
B.4L
C.5L
D.6L
E.7L
参考答案：B
We are very annoyed ______ his mistake, because we have emphasized this for several times.
A．at/about
B．with
C．on
D．to
地球和太阳之间的距离约是149500000千米，四舍五入到亿位约是（ ）亿千米．
A．1.5
B．1
C．1.4
D．0.1
