Which one?
Hello dear nstives

Which one do you pick?

I saw him while he was sitting and doing nothing but ......TV
1) watching
2) watch
3) to watch

Question

Which one?
Hello dear nstives

Which one do you pick?

I saw him while he was sitting and doing nothing but ......TV
1) watching
2) watch
3) to watch

Answer

"watch"  is the answer if you have seen the whole action.
"watching" is the answer if you saw just one part of his action of not doing anything.