他有时候非常固执。

He can be very ___stubborn sometimes.

她病了，但她太固执了，不肯去看医生。

She’s sick, but she’s too ___stubborn to see a doctor.

不管怎样，亚历克斯太固执了，不肯放弃，这就像对牛弹琴。

Anyway, Alex was too ___stubborn to give up and it was like talking to a brick wall.