问题补充：
The sales of houses in our city fell by 40 percent last month, 48 percent we don’t count low-price houses provided for poor residents.
A. as
B. unless
C. if
D. before
答案：
A. as
B. unless
(答案→)C. if
D. before
解析：考查连词和省略句：A. as当…时候，因为，正如，B. unless除非，C. if如果，D. before在…前面，句意：上个月这个城市的房屋销售下降了40%，如果不算上为贫穷居民提供的廉价房是48%。这句话是省略句，完整的是：The sales of houses in our city fell by 40 percent last month, The sales of houses in our city fell by 48 percent if we don’t count low-price houses provided for poor residents.选C。
