Answer:
B) The French believed it was untakeable.
C) It was located in a valley among the mountains in northwestern Vietnam.
Explanation:
The French garrison was believed by them to be undefeatable and they thought that preparing the battle on the Valley was a great strategic decision. The French troops overrated the Vietnamese troops and believed that they were not prepared and had no artillery to overcome them.
Because of that, the French troops were surprised when the Viet Minh troops attacked heavily the position and ended winning the battle.
It was one of the last battles of the Indochina War.
I hope this answer helps you.
