I want to know the answer to the following question:
Old Church Slavonic manuscripts were based on the local Slavic speech of what?
All the background I'm provided with is that "Slavic linguistic unity was to some extent visible as late as Old Church Slavonic manuscripts which, though based on local Slavic speech of Thessaloniki, could still serve the purpose of the first common Slavic literary language.". Is that enough to answer the question?