Why is mlk, rosa parks, harriet tubman, and colin powell considered heroes?

Martin Luther King Jr. was the voice for thousands of African-Americans. His famous letters and speeches are still talked about and he is admired as a hero, a great leader in the African-American civil rights movement.
Rosa Parks is a hero because she stood up for African-American civil rights, and was a brave, smart, and strong woman. She was given many honorable titles such as "the first lady of civil rights" and "the mother of the freedom movement". She is a hero for standing up for what he believes is right.
Just like everyone else in this list, Harriet Tubman is in history textbooks and is still very famous 'till this day. She was behind the brilliant Underground Railroad. She freed many slaves including her own parents and other family members. She risked her life many times for others in need. Colin Powell is known for being the first African-American to be appointed the secretary of state and for serving in the Army. All of these people will be remembered and admired forever. They will all be looked as heroes. 

The correct answer is b