Logical Breakdown

The problem gives us a clear conditional rule based on the number of players on a team. Let's analyze it.

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  Premise 1: All teams have between 5 and 15 players.
  


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  Premise 2 (The Rule): IF a team has more than 10 players, THEN they have reversible t-shirts.
  


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  Important Note: This rule only tells us for sure what happens when a team has 11, 12, 13, 14, or 15 players. It tells us nothing about teams with 10 or fewer players; they might or might not have reversible t-shirts.
  

Evaluating the Options

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  A. Teams that have 13 players have reversible t-shirts.
  
  This is True. A team with 13 players meets the condition of having \"more than 10 players,\" so the rule's consequence must apply to them.
  


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  B. Teams that have 12 players do not have reversible t-shirts.
  
  This is False. A team with 12 players also has \"more than 10 players,\" so according to the rule, they must have reversible t-shirts. This statement directly contradicts the rule.
  


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  C. Teams with 8 players do not have reversible t-shirts.
  
  This is Not Necessarily True. A team with 8 players does not meet the condition of having \"more than 10 players,\" so the rule does not apply. We have no information about them.
  


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  D. Only people on teams can have reversible t-shirts.
  
  This is Not Necessarily True. The information is limited to the teams in the tournament. It doesn't say anything about anyone else in the world.
  

Final Answer: The correct option is A because it is the only statement that is a direct and necessary conclusion from the given rule.