Final answer:
In the study with two-year-old 'Ben' having a conversation, the most likely occurrence is that he applies his own understanding of syntax to speak his own language, indicating cognitive growth in language development.
Step-by-step explanation:
In the study described involving two-year-old "Ben" and an adult having a conversation about candy, the likely scenario that occurs, based on developmental psychology, would be option 2: Ben uses his own understanding of syntax to produce his own language. At this stage in development, a child like Ben has typically learned a basic set of vocabulary and is beginning to form simple sentences, understanding more than he or she can articulate. This developmental milestone highlights cognitive growth, which includes the ability to form sentences using words that are part of their growing lexicon, and to express concepts within the limits of their language development. This process reflects children's capacity to internalize the grammar rules of their language, which sometimes leads them to make grammatical errors, such as overgeneralizing rules before they learn the exceptions.