Question

the cow is a useful animal​

Answer 1

Answer:

Cows or cattle are the most useful domestic animals. They benefit the humans and the environment in many ways that we fail to recognize or appreciate. They are raised as dairy animals for milk and other dairy products and as draft animals. Cow dung is also used as fuel all over the country.

Answer 2

Answer:

When a singular noun is meant to represent a whole class, the use of expression "The cow ..." is correct. One could also say "Cows are useful animals" to convey the same sense.

However, the indefinite article "a" is used in the given sentence in the sense of "any", to single out a cow as the representative of a class; as:

- A cow is a useful animal.