问题如下：
Frank Knight called variability that cannot be quantified at all as "unknown unknowns."
选项：
A. True
B. False
解释：
False because Frank Knight sets out a fundamental classification of "known" versus "unknown" risk in his classic paper on risk. Donald Rumsfeld, former US Secretary of
Defense said that "T here are things we know that we know. T here are known unknowns .. . But there are also unknown unknowns".
看不懂这道题能否解释一下？