The acid present in the stomach (a) kills the harmful bacteria that may enter along with the food. (b) protects the stomach lining from harmful substances. (c) digests starch into simpler sugars. (d) makes the medium alkaline.

Soln:

The answer is (a) kills the harmful bacteria that may enter along with the food.

Explanation:

The stomach consists of Hydrochloric acid, which kills the bacteria that enter through food. Thus stomach acid is helping in protecting us from harmful bacteria.