问题补充：
The flowers every day, or they will die.
A. must water
B. can be watered
C. should water
D. must be watered
答案：
A. must water
B. can be watered
C. should water
(答案→)D. must be watered
解析：此题重点考查被动语态，由于主语是动作的承受者，该句要用被动语态，排除A、C；根据句意：“每天一定要浇花，否则他们会死掉”B答案语气太委婉，因此要用must be+过去分词，故选D
