Answer:
A. you can make purchases even when you don't have cash
Explanation:
A credit card is used to buy things, you can pay those things when the "cut" of the balance on tour credit card is due, for example there are credita cards that give you a 28 days interests free day and you would have to pay it by the 4th of the next month, no matter when you buy it, for example if you buy a TV on the 25th of july, you have to pay your credit card on the 4th of august so it won´t generate interests, this could help you to buy things when you don´t have cash but you know you´ll have it by the next month.