_________is a blockchain based predictions market that uses the Ethereum blockchain.

Augur is a decentralized, blockchain-based predictions market built on the Ethereum network. It enables users to create and participate in markets based on the outcome of real-world events, using smart contracts to automate the process and secure transactions. Key Details: Ethereum-Based: Augur utilizes the Ethereum blockchain to facilitate the creation and settlement of prediction markets. It leverages Ethereum's smart contracts to ensure transparency, immutability, and trustless interactions. Decentralized Prediction Market: In Augur, users can bet on the outcome of various events, ranging from sports to elections. The decentralized nature of the platform ensures that no central authority controls the markets, providing a level of censorship resistance. Token Usage: Augur uses a token called REP (Reputation) that holders use to report and dispute outcomes of events on the platform. This ensures that the market outcomes are validated in a decentralized manner. Thus, A. Augur is the correct answer, as it is a blockchain-based prediction market built on Ethereum.