Answer: C. Ensuring that all of your credit card bills are paid on time
Explanation:
Paying your credit card balance in time will mean that you won't get charged interest or any other fees. This assumes there's no annual fee or any other kind of fee. It's possible with some cards that you can use them without any interest attached at all. Simply pay off the balance.
The credit card company banks on the fact that many people either can't or forget to pay off the month's balance, which incurs penalties and other fees. The credit card company also hopes that people pay the minimum monthly payment, which is the slowest way to pay off the debt and incurs the highest amount of fees. This option is definitely not recommended. So we can rule out choice D.
We can also rule out choices A and B. The goal is to have the lowest interest rate as possible. The lower the rate, the lower the interest if any applies. Choice B is a bad idea because you should have some cushion in your credit card balance.
