Which of the following is the earliest developing grammatical morpheme?

The earliest developing grammatical morpheme among the options provided is the present progressive suffix "-ing." This morpheme typically emerges during the early stages of language development in children, often appearing as they begin to combine words and express ongoing actions.

The use of "-ing" allows children to convey actions that are currently happening, which is a fundamental aspect of language acquisition. As children develop their verbal skills, they frequently start with simple action verbs and apply the "-ing" morpheme, demonstrating an understanding of action and temporality.

In contrast, other morphemes such as "-ed," which indicates past tense, and "-est," used for comparatives, generally develop later in a child's language learning process. The plural "-s" may appear earlier than past tense forms but still usually follows the acquisition of the present progressive "-ing." This developmental sequence reflects how children learn to express different time frames and relationships in their speech over time.