[DS] Ground firing at Air

I _think_ the answer to the following is yes, but I want to
make sure.

May a ground unit fire at an air unit on its' turn?  I'm
not talking about LAD or anything of that nature, just
on the tanks activation may it fire at a unit in the air
if it is within range?

On a similar not, may the same unit use opportunity fire
on a moving air unit?