一、二级单层、多层民用建筑之间的防火间距，不应小于（）米。
A、6
B、7
C、8
D、9
参考答案：A
In Township K, of the housing units are equipped with cable television. If of the housing units, including of those that are equipped with cable television, are equipped with videocassette recorders, what fraction of the housing units have neither cable television nor videocassette recorders ？（）
A.A
B.B
C.C
D.D
E.E
of the housing units are equipped with cable television. If 
of the housing units, including 
of those that are equipped with cable television, are equipped with videocassette recorders, what fraction of the housing units have neither cable television nor videocassette recorders ？（）