David invested $1,000 eight years ago and expected to have $2,800 today. He has neither added nor withdrawn any money since his initial investment. All interest was reinvested and compounded annually.

As it turns out, he has $3,200 in his account today. Which one of the following must be true?

Group of answer choices

He did not earn any interest on interest as he expected.

He earned a lower interest rate than he expected.

He earned simple interest rather than compound interest.

He earned a higher interest rate than he expected.