noun
BAD : When I took the two oranges out of the sack, I discovered that one of them was bad.
GOOD : When I took the two oranges out of the bag, I discovered that one of them was bad.
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sack = a very large strong bag: 'He's hurt his back trying to lift a sack of potatoes.'
bag = a container made of cloth, paper, leather etc: 'Somewhere in this shopping bag there's a bag of sweets.'