Which of the following sentences use commas correctly? Check all that apply.

When she returned to work after maternity leave, she learned that her office had been relocated to the second floor.

Not one employee was willing to sit at the desk, that had belonged to the man who turned out to be a serial killer.

Maurice listened to the team's proposal and then he promptly turned it down.

Please submit your proposal before October $18,2023.$

All participants must sign in register their vehicles and report to their assigned locations before $7$:$30.$