她是位出色的老师——她确实很精通自己的专业领域。

She's an excellent teacher - she really ___knows ___her ___stuff.

她从不怀疑自己的能力。她确实非常内行。

She never doubted her own abilities. She ___knew ___her ___stuff all right.

让他看看代码吧；在编程方面他真的很在行。

Ask him to look at the code; he really ___knows ___his ___stuff when it comes to programming.