operation on three images, one of the images is smaller than the others and they overlay each other

Here B and C cover the same area but A covers some parts of B and C.I want to do some operation where A covers the area. the final result from B and C should have the same size and extend as A.

A = imread('a.tif'); B = imread('b.tif'); C = imread('c.tif');

Betah =A ./ C;

and some more coding line.....