老师们，请教一下，完形填空题这里选sound为什么不行（知道这里选reply对，但不清楚选择sound为什么不可以）

One day in her senior year, I saw her sitting in the grass, head buried in her hands. I sensed her disappointment and I felt my own throat tighten. I sat down in the cool grass beside her and quietly asked what was wrong. "Oh, nothing," came a soft  29 (reply/sound). "I am just too short." The coach told her that at 5.5 feet she could probably never get to play for a top ranked team. She was heart broken.