Idioms are expressions with a meaning that isn't deducible from those of the individual words they contain. That is why these phrases should not be taken seriously.
In the given passage, we have an idiom<em> </em><em>a piece of cake. </em>When someone says that something was a piece of cake, they actually mean that something was easy, simple to accomplish. As the test turned out to be easy, Sari was positive that she did well.
I'm not sure if there were supposed to be options for us to choose from along with this question, but one conflict that arose during the Civil Rights Movement was segregation or Jim Crowe Laws.
