A. Orthoepy is not the study of correct grammar in conformity with established regional patterns. Orthoepy is actually the study of the correct or accepted pronunciation of words. Thus, statement A is incorrect.
B. Philology is not the study of phonemes and other characteristics of the systems of speech sounds in individual languages. Philology is the study of language in written historical sources; it is a combination of literary studies, history, and linguistics. Thus, statement B is incorrect.
C. Synchronic study pertains to the study of a language at a specific point in time, without considering its historical context. This means it analyzes the language as it exists at that moment. Thus, statement C is correct.
D. Diachronic study pertains to the study of language change over time. It involves looking at the historical development and evolution of languages. Thus, statement D is correct.
E. Phonology is the study of the system of sounds within a particular language or languages. It does not specifically focus on the cultural and social contexts of language, which would fall under sociolinguistics. Thus, statement E is incorrect.