-----HowoftendoIneedtowaterthehorses?      -----They

问题详情：

-----How often do I need to water the horses?

       -----They ________ water every day, or they will be thirsty.

      A. must give               B. mustn’t give

      C. must be given            D. mustn’t be given

【回答】

C

知识点：情态动词

题型：选择题