onsider implementing an immutable ADT called String for storing a piece of text like this ne$.$ Of the following potential methods to implement in String, which of the following is the east appropriate for an ADT to support?

String toUpper$()-$ returns a new string where all characters are upper case.

String trim$()-$ returns a new string where any spaces or newlines at the beginning or end of the original string have been removed.

char$$ getCharacters $-$ returns the array of characters that make up the string.

String concat$($String a$)-$ returns a new string which combines the input with the existing string to create a new string.