Clue: Second-commonest blood type: Abbr.

Answer: APOS

Length: 4

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Similar Clues:

• Blood types, abbr. (ABS with 3 letters)
• Like the rarer blood types, typically: Abbr. (NEG with 3 letters)
• Like some blood types: Abbr. (NEG with 3 letters)
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• Uncommon blood type: Abbr. (ANEG with 4 letters)
• Blood type letters (ABO with 3 letters)
• Blood-type letters (ABO with 3 letters)
• Blood type system (ABO with 3 letters)
• Blood-type system (ABO with 3 letters)