How did Ann Sullivan change Hellen Keller's life? Support your answer

Helen Keller who was deaf and blind, often got into uncontrollable tantrums and Anne Sullivan helped her come out of this, and learn subjects. She would write with her finger on Helen's palm and make her understand various topics. Thus, she gradually made Helen Keller disciplined.

Hardest. Just from the dictionary definition, it can only be either greatest or hardest. In the context of effort needed to solve a difficult problem, only "hardest" makes sense.