I accepted a _____ teaching students ages 6 to 12 with severe learning and behavioral ____ who’d moved from school to school.

A．position; difficulties

B．post; hard

C．job; troubles

D．occupation; difficulty

地下建筑起火后，由于浓烟()的弥漫，内部照明可能失去作用。

（A）火焰 

（B）毒气 

（C）湿度 

（D）空气