基础常用词
1. Difficult
通用词，适用大部分场景
例句：The exam questions were extremely difficult.
2. Hard
口语化，强调需要努力
例句：Climbing the mountain was really hard.
3. Challenging
隐含“有挑战性但可克服”
例句：The project was challenging but rewarding.
高强度/正式用词
4. Arduous
需长时间努力（体力/精神）
例句：The arduous journey took months.
5. Grueling
极度消耗精力（接近极限）
例句：She survived the grueling marathon.
6. Strenuous
强调体力上的高强度
例句：Avoid strenuous exercise after surgery.
7. Formidable
令人敬畏的困难（带敬佩感）
例句：He faced a formidable opponent.
复杂型困难
8. Complicated
因复杂而难处理（含冗余感）
例句：The instructions were too complicated.
9. Complex
结构复杂（中性描述）
例句：The complex machinery required expertise.
10. Knotty
棘手难解的问题（文学化）
例句：The team debated the knotty ethical issue.
情感消耗型
11. Taxing
精神/情感上的负担
例句：Caring for twins is emotionally taxing.
12. Demanding
需高度专注/投入
例句：Her job is highly demanding.
其他场景
Tough（口语，强调韧性）: The negotiation was tough.
Laborious（费时费力）: Writing the report was a laborious task.
Daunting（令人畏缩）: Starting a new career can feel daunting.
使用建议：
日常交流优先用 difficult/hard/challenging
书面语或强调强度时选 arduous/grueling/formidable
描述复杂问题用 complicated/complex/knotty
