在碱性条件下较稳定的水溶性维生素是（）
A.维生素B1
B.维生素B2
C.维生素B6
D.烟酸
E.抗坏血酸
参考答案：D
简述草原牧场沙化的防治措施？
Not until the war was over _______ to school.
A．that the children could go
B．the children couldn’t go
C．could the children go
D．the children could go
