Correct Answer - Option 2 : EC
The correct answer is option 2
The minimal set of the attribute which can uniquely identify a tuple is known as a candidate key.
Functional Dependency of R(A,B,C,D,E,F):
C → F, E → A, EC → D, A → B
Since C, E is not present on RHS of any functional dependency
C and E has to be present in any candidate key
(CE)+ = {C, E, F, A,D,B}