若电器和仪器着火，不宜选用（）灭火。
A、1211灭火器
B、泡沫灭火器
C、二氧化碳灭火器
D、干粉灭火器
参考答案：B
若|m－2|＋|n＋3|=0，则nm 。
By 16:30, ______ was almost closing time, nearly all the paintings had been sold.[ ]
A. which
B. when
C. what
D. that
