有一读者问这样一道选择题：
(1)_____ what to do next, she went to the girl for help.
A. Not having known B. Not knowing
答案是 B，为什么不可选 A?
这里应当选 B。knowing 意为“知道”，纯表静态。而 having known 则强调一种认识过程或一段经历，故在此不妥。注意下面的句子皆应用 know 的一般时态，不可用完成时态：
(2)I didn't know you were in London. How long have you been here? （know 表单纯“知道”）
(3)Do you know how to play chess? （know 表才能）
在下面的句子中始可用 know 的完成时态：
(4)How long have you known him?
(5)I have known him tell a lie.
(6)I can't believe that in the middle of the greatest prosperity this country has ever known a quality car won't sell.
