引起先天性水疝的病因是：（）
A.肾虚膀胱气化无力
B.水窦不行
C.脾虚生湿
D.寒湿外侵
E.肾阳不足
参考答案：B
Many scientists say that it’s important for us to have ______ food in our diet.
A．a variety of
B．a great deal
C．a large number of
D．a good many
