A fair coin is flipped 100 times in succession. Which of the intervals below is an asymptotic fluctuation interval at the 95\% confidence level for the frequency of appearance of heads on this coin?\\
a. $[ 0.371 ; 0.637 ]$\\
b. $[ 0.480 ; 0.523 ]$\\
c. [0.402; 0.598]\\
d. $[ 0.412 ; 0.695 ]$