Two factors that drive natural selection are listed below. 1. percentage of young that survive 2. ability to produce offspring which statement is true about the two factors?
a: factor 1 causes genetic variation and factor 2 causes differential reproductive success.
b: factor 1 causes differential reproductive success and factor 2 causes genetic variation.
c: both factors cause differential reproductive success.
d: both factors cause genetic variation.

answer fast plz i don't have much time.

Why do you think the puppy litter was all dark-haired?

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