It's a complete sentence, because it contains an action, an object, and a subject.
I think it's B. Possibly.
Answer:
Compound
Explanation:
You can split up this sentence into two sentences and it will still be grammatically correct.
They stopped at a better location with grazing for cattle and shops for wagon repairs.
They planned on going to Fort Laramie but decided to stop at Fort Bernard instead (10 miles east of Fort Laramie) because they were warned that Indians were fighting ahead, the grazing for cattle was poor at Fort Laramie, and they could get wagon repairs at Fort Bernard.
