The answer would be D, 7 hours of sleep
What is different with retroviruses in reproduction is that they do not kill their hosts at first because they can still insert their own genome. This process is what is known the reverse transcription. This is done by different proteins.
Biochemical stress is another factor fire
I'm just guessing since this is my prediction. Either B. or D. I dont know about C. and it is definitely not A. since the lumber companies are only taking down some trees instead of all of them.
Answer:
The populations become adapted to different environments and eventually become so different that they cannot interbreed to produce fertile offspring.
Speciation is the evolution of one species into two different kinds, and when they become isolated, that is the final step, since they cannot interbreed any longer.