The modern standard of time is
Option (A)
A second defined as 1/86, 400 of a mean solar day
Option (B)
A second defined as time constant of an RC series circuit having R=2 M ohm C = 50 pF
A second which is duration of 9192631770 periods of radiation corresponding to the transition between the two hyperfine levels of the fundamental state of the atom cesium 133
A second defined as 1/31556925.9747 of the time required by the earth to orbit the sum in the year 1990
Correct Option: