In what sense is the Hardy-Weinberg principle a null hypothesis, similar to the control treatment in an experi?

In what sense is the Hardy-Weinberg principle a null hypothesis, similar to the control treatment in an experiment?

a) Expected genotype frequencies can be calculated from observed allele frequencies and then compared with the observed genotype frequencies.
b) It defines what genotype frequencies should be if natural selection, genetic drift, gene flow, or mutation is occurring and if mating is random.
c) It defines what genotype frequencies should be if evolutionary mechanisms are not occurring.
d)It defines what genotype frequencies should be if nonrandom mating is occurring.