Before revision:  The business logic of a dApp (or part of it) is usually implemented within one (or more) smart contract(s) developed through Solidity, an object-oriented programming language for writing smart contracts on different blockchain platforms, including the popular Ethereum.
After revision:  The business logic of dApps is usually implemented within one (or more) smart contract(s) developed through Solidity, an object-oriented programming language for writing smart contracts on different blockchain platforms, including the popular Ethereum.