禅师让弟子思考这个公案：'未出生时的本来面目是什么？'

The master asked the student to meditate on the ___koan: 'What was your original face before you were born?'

禅师抛出一个公案，让弟子们打破常规思维。

The master gave his students a ___koan to break their habitual thinking patterns.