---Why didn’t you response to their greeting?---Sorry. I ______they ______ to me.A.don’t realize; are wavingB.don’t realize; were wavingC.didn’t realize; were wavingD.didn’t realize; are waving
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C解析这题考查时态，句意是：--你为什么不回答他们的问候？--对不起，我没意识到他们在向我挥手。所以是过去没意识到，另外主句是过去时，从句也是相应的过去时。选C。