I'm confused with this sentence correction question:
Hunters and warriors, bison were hunted by the native navajo, and they used the hides for shelters and meat for food.
a.bison were hunted by the native navajo, and they used the hides for shelters and meat for food
B. the native Navajo hunted bison, using the hides for shelters and meat for food
d. the native Navajo had hunted bison, and they used the hides for shelters and meat for food
A is obviously wrong because Navajo were hunters. But choice B and D are very close in their verb tense. I thought d is correct because "hunting" will happen before "using".
But correct answer is b
So I'm really confused about when to use past perfect