The genes carried by all members of a particular population make up the population’s
a. allele frequency.
b. phenotype.
c. genotype.
d. gene pool.

The correct answer is- D) Gene pool.

Gene pool is described as the collection or sum total of all the different genes present within a particular population ( group of interbreeding individuals) at a particular time.

On the contrary, phenotype represents the physical appearance or morphological form of an individual. Genotype is the genetic makeup of an individual and allele frequency is the frequency of a gene variant that is present at a particular locus in a population.        

Thus, option D) is the right answer.

b. the carbon cycle ensures living things have a source of hydrogen