Correct option is A
The correct idiom to fill in the blank is (a) "bury the hatchet."
Explanation: "Bury the hatchet" means to end a conflict or quarrel and become reconciled.
Example: After years of rivalry, the two teams decided to bury the hatchet and work together.
Meanings of other options:
Burn the midnight oil: To work late into the night.
Bark up the wrong tree: To make a wrong assumption about something.
Blow off steam: To release pent-up energy or emotions.