intractable

在现有理论下，这个挑战难以解决。

The challenge was ___intractable under existing theories.

这位病人因为不配合治疗，变得很难处理。

The patient became ___intractable due to refusing to cooperate with the treatment.

医生们发现他的头痛非常顽固，常规药物根本无法缓解。

The doctors found his headache was ___intractable, not responding to usual medications.