Which command would you use to determine the serial number used to apply for a Product Activation Key?

Which command would you use to determine the serial number used to apply for a Product
Activation Key?

A.
MDS-A# show license version

B.
MDS-A# show running-config | include serial-number

C.
MDS-A# show license serial-number

D.
MDS-A# show host-id

E.
MDS-A# show license host-id