Which sentence uses commas correctly?

AAt each stop, in the treasure hunt we found an envelope with a clue.
BAt each stop in the treasure hunt, we found an envelope with a clue.
CAt each stop, in the treasure hunt, we found an envelope with a clue.
DAt each stop in the treasure hunt we found an envelope with a clue.

Verified Answer :

The correct answer is B) At each stop in the treasure hunt, we found an envelope with a clue.
Since there is an inversion in this sentence (the regular order of words is shifted), there needs to be a comma after the first part.