---All of my old students took part in the party and some pop singers joined us as well．---It ________ a disappointing party．A.can’t beB.shouldn’t beC.mustn’t have beenD.couldn’t have been
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D解析上面一句用了一般过去时，说明此事发生在过去，后一句表示对过去事情的可能性的推测。因此应用D项，符合上下文的语境。