Read the paragraph.

Volunteering at the animal shelter in my neighborhood has been a very rewarding experience. I started volunteering with a good friend of mine during summer vacation last year. Volunteering at the shelter is a lot of hard work, and it isn’t always fun. Volunteers spend a lot of time cleaning out cages.

What does the gerund phrase "volunteering at the animal shelter” contribute to the text?

The phrase conveys significant interest and variety.
The phrase adds a specific detail about time and place.
The phrase acts as a noun that is the subject of the sentence.
The phrase adds more details by providing a direct object.