∵AB为圆O的直径，∴∠AEB=90°，又AE=BE，∴△ABE为等腰直角三角形，∴∠A=∠ABE=45°，∵AB=AC，∴∠ABC=∠ACB= 180°?45° 2 =67.5°，则∠EBC=∠ABC-∠ABE=22.5°．故选C．
