YOU SAID:

This event which occurred last month was so horrible

INTO JAPANESE

先月発生したこのイベントはとても恐ろしかったです

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This event that occurred last month was very horrible

INTO JAPANESE

先月発生したこのイベントは非常に恐ろしいものでした

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This event that occurred last month was very scary

INTO JAPANESE

先月発生したこのイベントはとても怖かった

BACK INTO ENGLISH

This event happened last month was very scary

INTO JAPANESE

先月起こったこのイベントはとても怖かった

BACK INTO ENGLISH

This event happened last month was very scary