In the Past Neutrinos Were Thought to Have Zero Mass

In the past neutrinos were thought to have zero mass.However,recent observations suggest that they have a small non-zero mass.One such observation is the electron neutrinos from the supernova 1987A which is 168,000 light-years from Earth.The neutrinos were observed within 13 seconds of each other.(Assume the supernova event occurred instantaneously.) This suggests that the difference in speed of the slowest neutrinos to the speed of light,c,is approximately

A) 0.13c
B) 0.87c
C) 10 ⁸c
D) 10 ¹¹c
E) 10 ¹⁶c