About 10,000 kilometers above the surface is the upper limit of the ________.
A) atmosphere
B) homosphere
C) troposphere
D) thermosphere
E) ionosphere
Question 2
The approximate boundary of the atmosphere extends outward at least ________ kilometers above the surface.
A) 1,000
B) 2,500
C) 5,000
D) 6,000
E) 10,000
