题目

Although ______ for many years, the two old sisters recognized each other at once. A. having been separated                   B. being separated C. having separated                        D. had been separated 答案：A 解析: A考查非谓语动词用法。前后主语一致并且前边动作发生在后面的动作之前，故用现在分词的现在完成时。a、b、c为有理数，且ab＞0，bc＜0，则ac＜＜0（填“＞”“＜”或“=”）