How many more unit tiles need to be added to the expression x squared plus 4 x plus 3 in order to form a perfect square trinomial?

To make x² + 4x + 3 a perfect square trinomial, take half of the x coefficient and square it: (4 ÷ 2)² = 4. The expression needs 4 unit tiles, and it already has 3, so add 4 − 3 = 1 tile. The correct choice is D, 1.

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