Answer: Option 'C' is correct.
Explanation:
Dominant traits are those traits which are visibly expressed in the organisms ( here, lizard)
Recessive traits are those traits in which genes are carried but it is not visible itself in the organisms.
Here, we can see that genes of Allele Z is carried by population of lizard in 50 years.
Here, it is natural selection acting on a dominant trait.
Hence, option 'C' is correct.