- a difficult problem/choice/task/language
- It will be very difficult to prove that they are guilty.
- Many things make it difficult for women to reach the top in US business.
- It is extremely difficult being a single parent.
hard : 含义广，通俗用词，与easy相对，泛指任何难理解，不好处理或不易做的事。
- There were some really hard questions in the exam.
- It's hard to say which of them is lying.
- It's hard being a single mother.
- Her handwriting is very hard to read.
- He's a hard man to please.
- The topics get harder later in the course.
- I feel sorry for the kids, too - they've had a hard time.