Instead of using tickets or swiping their smart phones, subway riders can smile at a screen to unlock the electric gates in about half a second after completing a ________ on Guangzhou Metro's official mini-program Guangzhou Metro mobile app. 地铁乘客无需购票或刷手机，只需在广州地铁官方小程序“广州地铁”手机应用上完成___________________后，对着屏幕微笑，即可在大约半秒钟内打开自动闸机。
A、facial recognition 面部识别
B、real-name registration 实名注册
C、fingerprint recognition 指纹识别