I think it’s b cause I done the quiz and I got all of them write
Answer:
Psychasthenia is a neurotic state characterized especially by phobias, obsessions, or compulsions that one knows are irrational.
A mule is a hybrid between a horse and a donkey (a male horse and a female donkey). Mules cannot produce offspring so it is under Hybrid Sterility, which falls under Letter D: a postzygotic barrier.
A postzygotic barrier diminishes the ability to reproduce of hybrid offsprings.
The decreased oxygen levels in the water will affect the respiration of the fishes. In order to cope up with the change, the fishes may migrate to a better place with higher levels of dissolved oxygen. This however does not relate to the process of natural selection as the fishes are still the same, genetically and phenotypically. Natural selection acts on those fishes that are able to survive the decreased oxygen levels. These fishes will breed and increase their numbers. The new generation of fishes will be tolerant to the lower oxygen levels. This new phenotype indicates a change in the genetic composition of the fishes.