----What do you know the of are the pig influenza in humans?
---- usually similar to regular human seasonal influenza .
A. symptoms
B. sympathy
C. symbol
D. symptom
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(答案→)A. symptoms
B. sympathy
C. symbol
D. symptom
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。