Chris needs to validate that a specific text box allows the text based on the three separate conditions that apply to the input: $($i$)$ it must consist of alphanumeric characters, $($ii$)$ the range for the total number of characters is between $3$ and $15,$ and, $($iii$)$ the first two characters must be letters. Based on the equivalence partition technique, what will be the valid equivalence classes that he can derive?

What is the correct answer $-$

a$.1.$ Part name is alphanumeric. $2.$ The first $2$ characters are letters. $3.$ The widget identifier has between $3$ and $15$ characters.

b$.1.$ Part name is alphanumeric. $2.$ The first $2$ characters are letters. $3.$ The widget identifier has greater than $15$ characters.

c$.1.$ Part name is not alphanumeric. $2.$ The first $2$ characters are letters. $3.$ The widget identifier has less than $3$ characters.

d$.1.$ Part name is alphanumeric. $2.$The first $2$ characters are not letters. $3.$ The widget identifier has between $3$ and $15$ characters.