3.It is strongly recommended that the machines _ be checked every year.
A.would
B.should
C.must
D.can
正确答案:B
解析:在 It is recommended/suggested/ordered/required 等结构后的 that 从句中,谓语动词需用虚拟语气(should + 动词原形),should 可省略。此处 machines 与 check 为被动关系,故用 (should) be checked。
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