The last one is punctuated the correctly.
A young person could join an activism group and help people who are often oppressed in various parts of the world like the LGBTQ+ community, or they could even go to protests and raise awareness about human rights or anything similar. They could even defend those who are attacked and prevent people from attacking them.
Tom Buchanan could be seen as a representative of the American Dream because his life is, for many, the ultimate goal. The American Dream is typically thought of as the possibility that, in America, anyone can start with nothing and, through their own hard hard work and perseverance, attain wealth and prosperity. Tom Buchanan is the pinnacle of wealth and prosperity; he has a lavish and elegant estate in East Egg, a beautiful and fashionable wife, and a team of polo ponies. Further, when people dream big—when they imagine what they would like to have and what they would like to be in their version of the American Dream—it could very likely be the success of someone like Tom that they imagine. Many people want all the things Tom has. People hope that achieving the American Dream will result in achieving Tom's life.
b Shane couldn't do anything about the leak