婴幼儿血维生素A水平低于多少μg／L即构成维生素A缺乏症（）
A.100
B.200
C.300
D.400
E.500
参考答案：B
I ______ follow you. Would you please repeat it?
A．can’t
B．mustn’t
C．needn’t
D．shouldn’t
The young ________ the hope of our country.
A．is
B．are
C．were
D．was
