I believe the answer is: serve at homeless shelters.
The help that given through a community service tend to target small/local area.
Service through army is for a nationwide area, so option A is wrong.
Signing up for peace corp is affecting world wide area, so option B is wrong.
Take part in teach America is a form of service with nation wide influence, so option D is wrong.
That leave us with serving at homeless shelters.
This is a little open for interpretation, but I would generally say that the best answer is that Josip Broz Tito was a very powerful leader, who kept the republics and the different groups together.
For example, we can see this from the fact that the first conflict happened in 1981: one year after his death ( a protest of Kosovans who demanded autonomy).
The Social Security Administration (SSA)
A date which will live in infamy—the United States of America was suddenly and deliberately attacked by naval and air forces of the Empire of Japan.