问题：
[单选题]男性，20岁。上前牙咀嚼时出现不适感1个月余。曾有过外伤史。半年前牙体变色。口腔检查：左右上1牙体变色，无明显龋损及其他牙体硬组织病变。牙髓活力测试无反应。叩诊（+）。X线片示：根尖部有圆形的透射影像，边界清晰，直径＜0．5cm，可能的诊断是（）
A、根尖周囊肿
B、根尖周肉芽肿
C、慢性根尖周脓肿
D、根尖周致密性骨炎
参考答案：
B
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