The eccentricity of an orbit with a major axis length of 100 million miles and a focal distance of 10 million miles is 0.1. Option D is correct.
The eccentricity (e) of an elliptical orbit can be calculated by dividing the distance the focal point (f) is from the center of the orbit by half the length of the major axis (a).
For the given orbit, the major axis length is 100 million miles and the focal distance is 10 million miles.
Therefore, the eccentricity is calculated as follows:
e = f/a
e = 10 million miles / 100 million miles = 0.1
So, the eccentricity of the orbit is 0.1.
Hence, D. is the correct option.