The most difficult to focust return component of commodity futures is?

CFA Level II Alternative Investments
#1

a. Spot return

b. Collateral return

c. roll return

The answer is A, but i cant figure out the rationale. Any takers? thanks

#2

Collateral return is known now

Roll return is a function of the term structure of the futures product (backwardation, contango)

Spot prices (in the future) have yet to be determined

#3

Thanks Galli.