What is the verb in this sentence: The dog jumped into the back of the truck.

Jumped.

Explanation:

A verb is usually an action, such as, walked or ran:

Let's identify the sentence step-by-step.

The dog jumped into the back of the truck - "The" is not an action.

The dog jumped into the back of the truck - a "dog" is not an action, it is a noun.

The dog jumped into the back of the truck - Have you ever jumped up and down? Probably. Jumping is an action word. It is showing someone or something doing something i. e., running, laughing, shouting.

So jumped is our verb in the sentence.

jumped

Explanation:

A verb is an action word, or something that you can do. Therefore, 'jumped' is the verb because it is the action that the subject (the dog) performs.