血中Hb含量低于多少时,即使重度缺氧,也难以出现发绀()

血中Hb含量低于多少时,即使重度缺氧,也难以出现发绀()

A.<50g/L

B.<60g/I(正确答案)

C.<70g/L

D.<80g/L

E.<90g/L

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