What is the length of the diagonal of the rectangle?

First we need to find the length and width of the rectangle.

As seen from the graph, the length is 4 units and the width of rectangle is 3 units. The triangle ABD is a Right Angled Triangle with side BD as the diagonal. BD is also the hypotenuse of the Right Angled Triangle, so we can find its length using the Pythagorean Theorem.

Using the theorem we can write: 



Therefore, the diagonal of the rectangle will be 5 units long.
So, the answer is option C