What is the term for the historical liturgical language, based on a South Slavic dialect, that contributed a large portion of formal and abstract vocabulary to the modern tongue?

• A Church Slavonic ✓
• B Old East Slavic
• C Proto-Slavic
• D Bulgarian

Church Slavonic was the written language of medieval Rus' and remains the liturgical language of the Orthodox Church; it provides a high-style layer of vocabulary distinct from everyday native words.