I may not be correct but I believe that Martin Luther King implied that if they were to protest with violent it would only result in more violence as a retaliation by the government. So by doing peaceful protest the government didnt have an actual solid reason to attack them, so when the government did enact violence on them it caught the attention of people around the world.
In medival times, the church was one of the most powerful forces in Europe. However, this lead to corruption and bribes, to the point where you could “buy a ticket to heaven” if you donated enough
I know for a fact that it was build to guard against the mongols, i'm not so sure about these two tho. It's the longest human made structure at more than four thousand miles, I want to say that two is also applicable
So the answers are 1,2,4
