(A) : The successful establishment of a species in a bare area is called invasion.
(R) : Invasion completes in three successive stages: migration, ecesis and aggregation.
A. If both (A) and (R) are true but (R) is not the correct explanation of (A).
B. If both (A) and (R) are true and (R) is the correct explanation of (A).
C. If (A) is true but (R) is false.
D. If both (A) and (R) are false.