We can solve this one by using the Pythagorean Theorem
Which is a^2+b^2=c^2
C is the hypotenuse, also known as segment AD.
To find the hypotenuse we do a^2, which is either of the two sides plus b^2 which is the other side
a^2 in this case is 4 units
and b^2 in this case is 4 units
4^2+3^2=25
we then take the sqrt if 25 which is 5
So segment AD=5
C is your correct answer