Which type of morpheme alters the form of a word to express grammatical features?

Inflectional morphemes are the correct answer as they specifically modify the form of a base word to convey grammatical information such as tense, mood, aspect, person, number, gender, and case. For example, adding "-s" to "cat" creates "cats," which indicates a plural form, or changing "walk" to "walking" to indicate a present participle.

These morphemes do not change the fundamental meaning of the word but instead provide essential grammatical context that helps to clarify the relationship between words in a sentence. In contrast, derivational morphemes typically alter the meaning or part of speech of a word, free morphemes can stand alone as words, and bound morphemes cannot exist independently, yet they do not primarily serve the function of grammatical modification. Thus, inflectional morphemes are specifically dedicated to signaling grammatical relationships.