Look for the largest square factor of 28. Since 28 = 4 × 7 and √4 = 2, we get √28 = 2√7. To simplify a surd, split the number under the root into a perfect-square factor and the remaining factor. Take the square root of the perfect square outside the radical. The expression is simplified when no square factor greater than 1 remains under the root. The correct answer is 2√7, which matches the calculation or reasoning shown.