Your hypothesis is incorrect considering every day has the same length to it.
Answer: A. Environmental drivers plus genetic variation in the population result in natural selection
Explanation: over geological time environmental conditions change. Organisms do not survive in one environmental niche with traits adapted to a possible future change that might suit those traits. Adaptation is not a matter of choice: adapt if possible or go extinct.
There is a (badly named) concept called pre-adaptation, which is that variations in some existing trait render adaptation to a different environment more likely.
It is not possible for Sarah and Thomas to develop cystic fibrosis but it would be possible for one of their children to inherit it. Both Sarah and Thomas are heterozygous and in a heterozygous pair of alleles the dominant allele is the one that will present. Because Sarah and Thomas both have the heterozygous allele combination Ff they are carriers which means that they will not experience symptoms of cystic fibrosis but they could pass cystic fibrosis onto one of their children.
