Answer:
option b ) is correct
Step-by-step explanation:
Let d be the distance in km from the place of lightning . velocity of sound is 340 m /s approx
in km/ s it is 0.34 km/s
time in sec taken by sound to cover a distance of d km
d / .34 = t
d = .34 t
d =

d = t / 3
so option b ) is correct . ,