ADJ-GRADED
(污漬)頑固的，難以去除的;(問題)棘手的，難以解決的
A stubborn stain or problem is difficult to remove or to deal with.
例句
This treatment removes the most stubborn stains...
這個方法能清除大多數頑固污漬。
The first and most stubborn problem was that of reductions in the number of aircraft.
最首要也是最棘手的問題是飛機數量的減少。