保密室有两道门，只有当两道门都关上时（关上一道门相当于闭合一个电键），值班室内的指示灯才会发光，表明门都关上了。图2中符合要求的电路是 （ ）
Some aspects(方面) of a teacher’s job ______ be tiring, and teachers often ______ work at inconvenient hours.
My friend, Tom, may have missed taking the flight to Africa, ______ he can’t arrive for another hour.
The sports meeting, due to ______ this weekend, has been put off due to the rain these days.
Researches are convinced ______ the positive effect of laughter ______ physical and mental health.
The ______ scene where the accident happened made him ______ to death.
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