"A" is a small frame tractor. They came in a conventional "style" like the "c" tractor.
And they also came in a rear engine rider. They are primarily devoted to grass mowing,
towing a small trailer and some models could fit a snow plow.
The "C" size tractor is a "garden tractor" and is capable of many tasks.....mowing,
snow blowing and plowing, rototiller, loader...etc.
Attachments do not interchange....except maybe the mower deck on
the conventional style "A". I do believe the hanger for the mower deck
would be different....I am not sure.
Buy an "A" if you have a small lawn and want to mow grass.
Buy a "C" if you want it to do everything else.