The H-W Law only applies to diploid organisms. Now you have to solve for p or q. It all fits, so you have equilibrium. This could be due to drift or selection.
Drift is sufficient to explain the changes in allele freq.
Environmental conditions, life styles, etc. must be very different in the two countries. Function of CF protein. There is only one gene here and different mutations are in different codons, so last two choices are out. The only way all the mutations could produce the same phenotype is if all prevent production of functional protein. There are multiple mutant alleles of the CF gene because there is more than one way to mess up the protein.