When Grid Power Goes Out, All Servers in a Rack

When grid power goes out, all servers in a rack lose power immediately. The server administrator confirms the servers have dual power supplies, which are connected to separate PDUs. Each of the PDUs is connected to a different UPS. Which of the following is the MOST likely cause of the problem?

A) Both of the UPS devices were set for the wrong voltage.
B) The power circuit was tripped on both PDUs.
C) The server power supplies failed during the outage.
D) The UPS batteries were discharged.