A gerund is a verb form that ends in -ing and functions as a noun. In the given options, the sentences that include gerunds are:
- "Swimming in the gulf is Finn's favorite summer activity."
- "While swimming at the beach, Harper found a starfish."
- "Nash has been swimming since he was five years old."
So, the sentences that include gerunds are the first, second, and fourth sentences. The correct response to your question is:
- Swimming in the gulf is Finn's favorite summer activity.
- While swimming at the beach, Harper found a starfish.
- Nash has been swimming since he was five years old.
If you are looking for one response, you can choose the first one.