井下有害气体硫化氢（H2S）的最高允许浓度是（）%。
A.0.0024
B.0.00025
C.0.00066
D.0.0066
参考答案：C
Tom didn't go hiking with his classmates ____ his illness. [ ]
A. because
B. because of
C. as
D. since
异烟肼引起中枢神经症状的原因是（）
A.异烟肼本身所致
B.异烟肼抑制PABA的合成
C.异烟肼抑制GABA的合成
D.异烟肼减少体内维生素B6含量
E.异烟肼代谢产物所致
