These machines must ______ before they are used.A、checkB、be checkedC、are check

游客2025-07-04 4

问题 These machines must ______ before they are used.

选项 A、check
B、be checked
C、are checked

答案 B

解析仍然是考查被动语态，注意must 是情态动词，后面应接动词原形be。

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