Answer:
setCharAt()
Explanation:
StringBuilder is a dynamic object that allow to create the string with no size restriction.
To answer the question, let discuss each option.
Option a: insert()
insert function is used to insert the element at the specific location but it does not change the rest of the character.
Option b: setCharAt()
it is used to change the value at specific location, it takes two argument location and character.
Option c: append()
it is used to connect the two string but it does not change the rest of the character.
Option c: charAt()
it is used to get the character at specific location. it does not allow the change.
Therefore, option b is correct option.
