Why can't I use "eating?" How is that incorrect? Isn't "eats" and "eating" the same if used in present tense?
Unfortunately, it is technically different. The phrase "is eating" would be considered present progessive tense as opposed to just present tense which would be "eats".
"The man eats sandwich"
A universally true statement there.
ooh that voice crack sksksk
"The man eats sandwich" should not be marked wrong as it only means the same with "The man eats a sandwich"both in tense and english grammar rules.