I'd say letter c) One of America's best-loved exports is jazz...
Why? Compound words are made up of two or more words that are combined to create a new word with a distinct meaning. And that is just what "Best-loved" is. As you might know. "best" is an adjective describing something that is superior, and "loved" is a verb indicating that someone has a feeling of deep affection or admiration for something. However, it could potentially be confusing or ambiguous in some cases.