Final answer:
To write a sentence and underline the subject, you need to identify the subject as the noun or pronoun that performs the action or is being described.
Step-by-step explanation:
In order to write a sentence and underline the ______, you need to identify the subject. The subject is the noun or pronoun that performs the action or is being described in the sentence. For example, in the sentence "The cat is sleeping on the mat," the subject is "cat."
Choosing the correct noun as the subject is essential to ensure the sentence is grammatically correct and makes sense.
So, in the given sentence, the noun that serves as the subject should be underlined.