What does a bound morpheme require in order to convey meaning?

A bound morpheme specifically requires the presence of other morphemes to convey meaning because it cannot stand alone. Bound morphemes typically attach to free morphemes (words that can stand alone) to form words or modify meanings. For instance, in the word "cats," the suffix "-s" is a bound morpheme that indicates plurality; it does not have meaning by itself and relies on the free morpheme "cat" to convey the full concept. This interplay between bound and free morphemes is a critical part of understanding morphological structures in language. The other choices do not accurately capture the nature of bound morphemes: they do not stand alone, they are not always standalone words, and they are not limited to being suffixes as they can also be prefixes or infixes.