We've just installed two air-conditioners in our apartment, ______ should make great differences in our life next summer.[2002]

【正确答案】 A

【答案解析】解析：非限定性定语从句起补充说明作用，用逗号与主句隔开，which充当该从句的引导词，所以A为正确答案。what引导名词性从句，作主语和宾语；that不可引导非限定性定语从句；they不是关系代词，不能引导定语从句。