Results of scientific research suggest that play a major role in the aging process by serving as biological clocks that control the number of times cell division can occur.

It is the telomeres that play a major role in the aging process by serving as biological clocks that control the number of times cell division can occur. 

A telomere is a district of tedious nucleotide groupings at each end of a chromosome, which shields the finish of the chromosome from disintegration or from combination with neighboring chromosomes. 
Be that as it may, there are as yet genuine questions about whether turning around or backing off maturing by means of telomerase action is the appropriate response. Since while telomerase lengthens telomeres, in people with disease, the protein enables existing tumors to become speedier.

The correct answer is "b"