Which one of the following statements must be true?

Each card in a set of fifteen cards has one of three shapes on it: a triangle, a square or a circle. Inside the shape a number from 1 to 9 is written. No two cards are identical.

The only number that appears in both a square and a circle is 7.

Which one of the following statements must be true?

Each shape appears on five cards. There are at least five cards with circles on them. There are at least five cards with squares on them. There are at least five cards with triangles on them

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Which one of the following statements must be true?