Answer:
serve at homeless shelters.
Step-by-step explanation:
The answer is
"serve at homeless shelters."
Community service means offering service to the people in the neighborhood or nearby place. It means serving a small group of people or a small place.
Other options are wrong because all these options shows service to the entire nation. All the other options whether to join the the US Army or US Navy, or signing up for the Peace Corps, or to take part in Teach for America campaign means offering service to the entire nation as a whole and not to a small community.
Thus the correct answer is
"serve at homeless shelters."