Until 20-30 Years Ago, People with Cystic Fibrosis (CF) Wouldn't

Until 20-30 years ago, people with cystic fibrosis (CF) wouldn't live long enough to reproduce. CF is a homozygous recessive condition, leading researchers to think that, over time, the incidence of CF would decrease because the allele would be removed from the gene pool. The results actually indicate that the rate of CF is on the rise. Based on what you know about why certain genotypes and phenotypes persist in a population, which of the following could be a likely explanation for why the rate of CF is on the rise?

A) We are being subjected to more mutations as a population due to more pollution.
B) The population is increasing, and more people mean more mutations.
C) The heterozygous condition is beneficial, much like what we see with sickle cell trait.
D) People are traveling more, so when people from different areas reproduce, more mutations will result.