第6题: [单项选择]I don't remember______to Professor Brown during my last visit to Harvard. A. having introduced B. having been introduced C. to have introduced D. to have been introduced 参考答案:B 答案解析:[考点] 动名词作宾语 [解析] 动词remember后接不定式,表示后面的动作发生在remember这个动作之后;如果后面的动作发生在remember之前,则用“动词+ing”。本题中i
第7题: [单项选择]通常全数字电力线载波机高频调制方式为() A. 改进型交错四相相移键控(OQPS) B. 频分复接(FDM) C. 模拟调制(单边带SSB) D. 时分复接 参考答案:A