他有时可能非常固执。

He can be very ___stubborn sometimes.

他们经常大吵大闹，因为两人都太固执了。

They have massive rows because they're both so ___stubborn.

不管怎样，亚历克斯太固执了，不肯放弃，就像对牛弹琴。

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