1. 不可数名词（单数形式）
表示广义的“困难、费力”，不可数，无复数形式。
结构：`difficulty (in) doing sth` 或 `have difficulty with sth`
例句：
She had difficulty solving the math problem.
We faced difficulty accessing clean water.
2. 可数名词（复数形式：difficulties）
表示具体的困难或难题（多个或不同类型），可数，复数形式为 difficulties。
例句：
The project was canceled due to financial difficulties.
They discussed the difficulties of living abroad.
3. 常见错误与对比
❌ 错误：I have many difficulty in learning English.
✅ 正确：I have difficulty learning English. （泛指困难）
✅ 正确：I encountered difficulties while writing the essay. （具体难题）
4. 固定搭配
`without difficulty`（轻松地）
He finished the task without difficulty.
`run into difficulties`（遇到困难）
The team ran into difficulties during the experiment.
总结：
单数：抽象概念（整体困难）
复数：具体问题（多个挑战）
根据语境选择形式，避免混淆！
