Final answer:
In Roger Brown's framework on language development, 'Operations of Reference' involve indicating objects or people, with 'demonstrative' being the classified sentence type in this category.
Step-by-step explanation:
The question refers to Roger Brown's stages of language development. Specifically, it is asking about the sentinel types of sentences classified under "Operations of Reference" in Stage I, as per Brown's 1973 research on first language acquisition. Options listed in the question such as 'negative', 'interrogative', 'action', and 'demonstrative' represent different linguistic functions or sentence types. For Roger Brown, operations of reference are about how speakers use language to refer to things and would include pointing out or indicating objects or people. Therefore, the 'demonstrative' option, which involves using words like 'this' or 'that' to point to specific things, would be classified under operations of reference in Roger Brown's framework.