Which of the following is included in Brown's Morphemes Stage 2?

Brown's Morphemes Stage 2 specifically focuses on the early grammatical developments in children's language acquisition. At this stage, one of the key morphemes that children begin to use is the present progressive form, marked by the addition of "-ing" to verbs. The present progressive indicates ongoing action and is one of the first grammatical constructions that children typically master as they start combining words into more complex sentences.

This stage is characterized by children's ability to start forming more intricate sentences while demonstrating an understanding of verb tenses and aspects, making the present progressive vital for expressing actions in progress. The acquisition of this morpheme aligns with the developmental milestones outlined in Brown’s stages, where children begin to engage in more sophisticated narrative structures.

The other choices pertain to different stages of language development. Irregular past tense forms, third person regular present tense, and articles are acquired later in Brown's stages of grammatical development. Therefore, the inclusion of the present progressive "-ing" in Brown's Morphemes Stage 2 highlights its significance in early language development and is correctly identified as part of this stage.