The digestive juices break down into simpler substance
A. Proteins
B. Hydrochloric acid
C. Fatty acid
D. None of the above

Hint: Hydrochloric acid activates pepsinogen to form enzyme pepsin which then helps in digestion by breaking down the bonds which link amino acids and this process is termed proteolysis.

Complete answer:
Digestive juice or fluid is the gastric acid which is formed in the stomach and it is composed of HCl i.e., Hydrochloric acid, KCl i.e., potassium chloride and NaCl i.e., Sodium chloride.

Gastric acid plays an important role in the digestion of proteins where it breaks down the simpler substances by activating the digestive enzymes, and making ingested proteins unravel so that digestive enzymes break down the long chain of amino acids.

Due to the highly acidic environment in the stomach, lumen causes the protein to lose their folded structure and become denatured and this exposes the protein’s peptide bonds.

If we look at options now,
> Option A - Proteins.
It is the correct option since digestive juices break down proteins or amino acids into simpler substances.

> Option B - Hydrochloric acid.
Digestive juice is HCl present in the stomach then how can it break itself. This option is therefore incorrect as the gastric acid present in the stomach breaks down proteins.

> Option C - Fatty acid.
This option is also incorrect since there is breakdown of amino acid not fatty acid.

Hence, the correct answer is option (A).

Note: There is proteolysis done where there is breakage of bonds which forms amino acid and due to the gastric acid i.e., HCl breaks down the proteins into simpler substances. This is due to activation of digestive enzymes i.e., pepsin.