Possible answers are
-by a small number of heterozygotes in the population
-by a small population size
-by large numbers of homozygous dominants
-by a large number of homozygous recessives
-any of the above
The correct answer is by a large number of homozygous recessives
When frequent mating of genetically similar individuals occurs in a population, that population faces a great risk of inbreeding depression.
When there is a lot of inbreeding ( mating of the individuals that are close relatives) within a population, certain alleles which are usually rare now can become very abundant.
What this means is that in a small, inbred population the recessive alleles (often carrying a risk of diseases and suboptimal traits) become more abundant.
When we analyze the genetic structure of a population and we find a lot of homozygous recessive individuals, we can safely conclude that this population is facing inbreeding depression.