饮水型地方性氟中毒主要是由于下列哪项而引起()
A.食物氟污染浓度高
B.土壤中氟含量过高
C.饮水氟含量过高
D.饮水氟含量过低
E.维生素A和钙缺乏
参考答案:C
Mother told me _____ too much time reading novels.[ ]
A. don't to spend
B. don't spend
C. not to spend
D. not spend
预制板在墙上的搁置长度不少于()mm。
A.110
B.80
C.90
D.100