There is a deck of cards, each of which has a number on one side of the card and a letter on the other side. This fact is a given, and you can assume it is true. Four of these cards are dealt onto a table, showing the following face up:

**Conjecture: Read this CAREFULLY: ** "For these four cards, every card with a vowel on one side has an even number on the other."

**Question:** What is the smallest set of cards (list which ones) that must be turned over to test the conjecture?

**Definitions:** * Vowel* = a letter in the set {A, E, I, O, U}

*Even Number* is divisible by 2 without remainder,{...-4, -2, 0, 2, 4,...}

*Test:* An experiment that would refute (disprove) the conjecture, if the conjecture were false.

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