那次经历使我难以忘怀。

The experience made an indelible impression on me.

《牛津词典》

那个事件令我难以忘怀，因为那是我看到的那个国家的第一例种族歧视事件。

The incident stuck in my mind because it was the first example I had seen of racism in that country.

《柯林斯英汉双解大词典》

童年时的那种幸福是我难以忘怀的。

The kind of childhood well-being is my unforgettable.

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