Because insulin and are secreted in the bloodstream in equal amounts, can be used as a clinical indicator of endogenous insulin production.

c-peptide

Explanation:

Insulin is an hormone in our body which is produced by pancrease's beta cells. Insulin helps in regulation of blood sugar level. It helps body to use glucose taken through meal or store glucose for further future activities. Insulin is made up of peptide chains bonded by di sulfide bond and when the two chains separates C-peptide is released.

i am positive it is c. condensing but i may be wrong

d. cellulose and starch