【答案】The plants must________ every three days, or they will fail to grow.

The plants must________ every three days, or they will fail to grow.

A. water B. watering C. be watered D. watered

【答案】

C

【解析】

句意：这些植物必须每三天浇一次水，否则它们就不能生长。考查被动语态。must一定，情态动词后接原形动词。plants是动词water（浇水）的受动者，需用被动语态，即“be+过去分词”结构。根据句意结构和语境，可知选C。