Using full stop increments, what are 3 sets of equivalent exposures for f/4 - 1/250?
a) f/8 - 1/125, f/5.6 - 1/250, f/2.8 - 1/500
b) f/2.8 - 1/60, f/5.6 - 1/125, f/11 - 1/250
c) f/16 - 1/500, f/11 - 1/250, f/8 - 1/125
d) f/4 - 1/250, f/8 - 1/125, f/16 - 1/60
