Answer:
D.

Explanation:
We can see the shape can be cut into 4 right triangles. We can use pythagoreans theorem to find the length of the hypotenuse.
The distance from 0 to a represents one side, and the distance from 0 to b represents the other side.
So

(C represents the hypotenuse)
So the hypotenuse can be written as

Since four of these lines make up the perimeter,
the total perimeter will be
