What is the compatibility of DDR3 and DDR4 DIMMs in the same HP Workstation?

A.
the system can have any number of DDR3 and DDR4 DIMMs

B.
the system must have at least 2 DDR4 to one DDR3 DIMMs

C.
the system must have at least one DDR3 to one DDR4 DIMMs

D.
the system must have either all DDR3 or all DDR4 DIMMs