A person looking down a long, straight highway sees an automobile coming toward her at night. Howfar away is the car when the headlights can just be resolved as two separate light sources if they are 1 : 6 mapart? Assume the pupil of her eye is 4 : 0 mm in diameter and the light has a wavelength of 5 5 0 nm .
a . 4 2 km
b . 1 : 3 km
c . 1 7 km
d . 9 : 5 km
e. 4 : 6 km