a. impossible to forget
a. 忘不了的, 令人难忘的
1. This vacation was unforgettable because of the beautiful scenery.
这次假期因为美丽的风景而令人难忘。
2. She gave an unforgettable speech that inspired everyone in the audience.
她发表了一场令人难忘的演讲,激励了在场的每一个人。
3. We had an unforgettable time at the concert last night.
我们昨晚在音乐会上度过了一个难忘的时光。