question: What are the QF-4 aircraft being replaced by the US Air Force ?
answer: early model F-16 aircraft converted to QF-16 configuration
turker_answer: The US Air Force is replacing the QF-4 aircraft with an early model F-16 aircraft converted to QF-16 configuration .
rule-based: The QF-4 aircraft are being replaced early model F-16 aircraft converted to QF-16 configuration by the US Air Force .