Answer:
Option A -

Explanation:
Given : A square on a coordinate plane is translated 9 units down and 1 unit to the right.
To find : Which function rule describes the translation?
Solution :
Let's (x, y) is coordinate plane.
x represents the horizontal move and y represents the vertical move.
There is a shift 'a' unit downward

There is a shift 'b' unit right

It is translated 9 units down and 1 unit right.

Therefore, Option A is correct.