汽油精制中氢氧化钠的作用是脱除（）、助催化剂。
参考答案：硫化氢
The water in the river smells terrible, people must ______ dirty things into it. [ ]
A. be stopped to throw
B. be stopped from throwing
C. stop to throw
D. stop from throwing
根据心绞痛的严重程度可分（）
A.4级
B.2级
C.5级
D.3级
E.6级
