单选题 If the United States had built more homes for poor people in 1955, the housing problems now in some parts of the country ______ so serious.
A. wouldn't be B. wouldn't have been
C. will not be D. would have not been

【正确答案】 A
【答案解析】[解析] 本句使用了虚拟语气，但要注意的是：在这里从句使用过去完成时，表示对一般过去条件的虚拟；而主句使用一般过去时，表示对一般现在情况的虚拟。做题时，注意到主句中的now是很重要的。