6394. He took a momentous decision in this case.

✅ The correct answer is option B.
Transient : lasting only for a short time; impermanent.

Important : of great significance or value.

Wrong : not correct or true; incorrect.

Hopeless : feeling or causing despair.

Momentous : of great importance or significance, especially in having a bearing on future events.

Synonym of Momentous is Important