How to identify the Subject In this sentence

[Uva@90]

The combination of growth and return on invested capital (ROIC) relative to its cost are what drive value.

A. The combination of growth and return on invested capital (ROIC) relative to its cost are what drive value
B. The combination of growth and return on invested capital (ROIC) relative to their cost is what drives value
C. The combination of growth and return on invested capital (ROIC) relative to its cost is what is driving value
D. The combination of growth as well as return on invested capital (ROIC) relative to its cost was what drove value
E. The combination of growth and return on invested capital (ROIC) relative to its cost is what drives value

[DavidG@VeritasPrep]

The combination of growth and return on invested capital (ROIC) relative to its cost are what drive value.

A. The combination of growth and return on invested capital (ROIC) relative to its cost are what drive value
B. The combination of growth and return on invested capital (ROIC) relative to their cost is what drives value
C. The combination of growth and return on invested capital (ROIC) relative to its cost is what is driving value
D. The combination of growth as well as return on invested capital (ROIC) relative to its cost was what drove value
E. The combination of growth and return on invested capital (ROIC) relative to its cost is what drives value

The subject = the combination. So we want The combination .... is

("Of growth and return...." is a modifier. Just be aware that are instances in which the modifier will dictate whether the subject is plural. (If, for example, the subject is "some," "percentage," "most," etc.) For example, "Some of the pie is missing." Vs. "Some of my friends are taking the test.")