29.【2019河南南阳】The flowers _____every day, or they’ll die.
A.can be watered                            B. should water        
C. must be watered                           D. water
【答案】C
【解析】试题分析：句意：这些花必须每天都浇水，不然会死去。句子要用被动语态，其结构为be+动词过去分词；如果前面有情态动词，be用原形；情态动词can能够；must必须；结合语境故选C。
30.【2019河南济源】In order to make Chongqing more beautiful, lots of trees _____ on both sides of the street.
A. should build                              B. have built          
C. must be built                              D. will build
【答案】C
【解析】本题需要的是被动语态，主语是被发生的，是动作的承受者，只有C为被动语态结构，其余的选项，都是主动语态，故选C
31.【2019辽宁大连】--- So far this year,many new houses_____ in this area with the help of the government.
--- It’s great.
A. Build               B. are built            C. will build         D. have been built
【答案】D
【解析】本题考查的是现在完成时的被动语态其结构为主语+have been+过去分词，故选D