We met a boy _______ a heavy bag.
We met a boy _______ a heavy bag.
Explanation
"Carrying a heavy bag" describes the boy, so a present participle is needed to act as an adjective.
"Carrying" shows the action happening at the time we met the boy.
"Carrying a heavy bag" describes the boy, so a present participle is needed to act as an adjective.
"Carrying" shows the action happening at the time we met the boy.