小负荷时，混合气的数量和品质比怠速时有所提高，因此要求混合气比怠速时浓。（）
参考答案：错
Tom _______ his homework at home. [ ]
A. doesn't
B. don't do
C. don't does
D. doesn't do
泡沫泵站与保护对象的距离不宜小于（）m。
A．60
B．50
C．30
D．25
