----What do you know the _____ of are the pig influenza in humans? ----usually similar to regular human seasonal influenza .A.symptomsB.sympathyC.symbolD.symptom
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A解析考查名词词义辨析。句意：你知道人类感染猪流感后的症状吗？通常与患流行性感冒症状相似symptom症状符合句意;sympathy同情；symbol符号。从what are可以看出是复数名词。