Consider the following procedures for string manipulation.

Procedure Call Explanation

concat$($str$1,$ str$2)$ Returns a single string consisting of str$1$ followed by str$2.$ For example, concat$("$key$",$ "board"$)$ returns "keyboard".

prefix$($str$,$ length$)$ Returns the fir

st length characters of str or str if length is greater than the number of characters in str$.$ For example, prefix$("$delivery$",3)$ returns "del" and prefix$("$delivery$",100)$ returns "delivery".

The variable initials is to be assigned a string consisting of the first letter of the string firstName followed by the first letter of the string lastName. Which of the following assigns the correct string to initials $?$