硫化氢监测仪使用过程中（）校验。
A.检查时
B.要定期
C.要不定期
D.要随时
参考答案：B
His health failing, ____ last year.
A．so the school gave Mr. Smith leave
B．the school had given Mr. Smith leave
C．so Mr. Smith went on leave from work
D．Mr. Smith went on leave from work
EDI
