What is the adjective in sentence Three turtles swam pond?

There is no adjective in the sentence "Three turtles swam pond".

Here's why:

* Adjectives describe nouns. We have the noun "turtles", but "three" is a quantifier (telling us how many) and "pond" is another noun.

* "Swam" is a verb.

To make this a complete sentence with an adjective, you could say:

"Three large turtles swam in the pond."