A. can't be split across multiple files, everything should be in one single file.
B. can be split across multiple files, but every contract must be in a file with the same name as the contract itself.
C. can be spread across multiple files. To import all contract from a file you can use "import 'myfile.sol'. To import Contract MyContract from myfile.sol you use "import {MyContract as SomeContract} from 'myfile.sol';".
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