What does the "Combined" power redundancy mode in the Nexus 7000 protect from occurring?

What does the “Combined” power redundancy mode in the Nexus 7000 protect from occurring?

A.
One PSU failure

B.
Lack of redundancy

C.
One input circuit failure

D.
One PSU or one input circuit failure

Explanation:
According to the DCUCD training material, page 2-17:

There are three modes of power supply redundancy:

Combined mode (nonredundant)
= combining all power supplies, if any power supply fails, some or all components may be affected

N+1 redundancy
= enables the Cisco UCS to tolerate failure of any single power supply

Grid redundancy
= enables the Cisco UCS to tolerate a loss of an entire power grid within the Data Center if properly cabled