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ID14-Singles and Pairs Must be Self-Picked Unless Ready to Win
Question: Can I call a tile if I am playing a Singles and Pairs hand?
Answer: The Singles and Pairs category consists of all concealed hands, therefore you cannot call a tile during the game. The exception to this rule is that you may call the last tile, which would be your 14th tile, needed to complete Mah Jongg.
Sources: Mah Jongg Made Easy 2020 page 15 para 2