It Has Been Suggested That a Fundamental Physical Unit of Time

Multiple Choice

It has been suggested that a fundamental physical unit of time is the time required for light to traverse the diameter of the nucleus of an atom (approximately 3 $\times$ 10^-13 m) .This unit of time is approximately

A) 1 s
B) 10^-4 s
C) 2 $\times$ 10^-20 s
D) 10^-21 s
E) 10^-23 s