All organisms with unlimited resources exhibit exponential population growth. with this growth, how long would it take for a pair of fruit flies to have enough offspring to cover the entire earth?

one year

Explanation:

An average fruit fly could grow into fully adult form in 40 - 50 days (in this point , they are ready to reproduce ).

One fruit fly could lay around 500 eggs in one go and they have multiple partners around their life time.  This number make it impossible for humans to control fruit fly population and it's predicted that they can cover the entire earth with just one year period.

answer; (d) one tectonic plate plunges beneath another; (most common,convergent boundaries)