问题补充：
The river smells terrible. People dirty things into it .
A. must stop to throw
B. must stop from throwing
C. must be stopped to throw
D. must be stopped from throwing
答案：
A. must stop to throw
B. must stop from throwing
C. must be stopped to throw
(答案→)D. must be stopped from throwing
解析：考查推测，must have done表示对对去事情的肯定推测，名词People和动词词组stop from是动宾关系，所以用被动式，句子意思“河水很难闻，人们一定是把脏东西仍在河水里”,所以选D
