题目

--Did you hear something? --No. I ______ but I ______ anything at all. A. listened; have heard                 B. have listened; hear C. am listening; hadn’t heard           D. was listening; couldn’t hear 答案：D生活中常见的聚酯纤维(的确良)的结构简式如图所示：它是由乙烯和对二甲苯经过一系列反应后的产物缩聚而成的，则合成过程中乙烯和对二甲苯的物质的量之比为( )A．1:1 B．2:1 C．1:2 D．3:1