1. which of the following statements best describes the relationship between the hardy-weinberg principle and the effects of natural selection?

The answer is the second option. 

The Hardy-Weinberg equation assumes that all genotypes occur with equal frequency, if selection can be quantified, relative fitness values can be calculated and used to appropriately modify the Hardy-Weinberg equation.
Choices to this question are: 
1---but if there is selection against one or more genotypes, equal frequency of all genotypes is not possible.
2If selection can be quantified, relative fitness values can be calculated and used to appropriately modify the Hardy-Weinberg equation.
3Natural selection can influence the genotype frequencies predicted by Hardy-Weinberg, but allele frequencies are not affected.
4If it can be determined that selection favors a particular genotype, the Hardy-Weinberg equation should not be applied.

Since you did not present any choices for this question, I'll just answer you the relationship between the Hardy-Weinberg principle and the effects of natural selection.

The Hardy-Weinberg principle states that the frequency of genotypes and alleles in genetics of a certain population does not change in generations unless there is an influence of evolutionary change. In this case, one of these evolutionary changes is natural selection or the the tendency of the animals to choose a mate for survival of species.