Which best describes why heat pumps are reversible? a. they can heat and cool an indoor space. b. they involve a metal expanding or contracting against another. c. they combust and can also add coolant. d. they allow a piston to move up and down.

A. They can heat and cool an indoor space.

1) gene flow

- it is described as the transfer of genes from one population to another population so that frequency of gene is increased.

-a zebra migrates to join a different herd of zebras.

2) natural selection

- a mechanism of evolutionary change in which individuals with advantageous traits survive and reproduce whereas the others ( those that can not adapt) eliminate from the population.

-competition for sunlight leads to taller trees.

3) mutation

- permanent change in the nucleotide sequence of dna ( genetic material) that could have harmful or useful consequences.

-the dna of a snake changes to make its venom stronger.

4) genetic drift - it is a random phenomenon ( that occurs by chance such as fire) that results in change in the gene frequency in a small population.    

-a grassfire randomly sweeps through a population of buffalo and kills most of the animals.

explanation:

population. population is the number of people or animals in a particular place. an example of population is over eight million people living in new york city.

here is your answer hope i .