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More recently, Rolls-Royce and IHI Corp. have begun working on a joint future fighter engine demonstrator, which will build on IHI’s work on its advanced XF9-1 experimental powerplant and Rolls-Royce’s work on the XG240, the power system destined for the Tempest

はっきり書いてあるから1が正解
実物なのか設計段階のものなのか知らんけど