(A) : Lichens cannot be the pioneer species on a bare rock.
(R) : They are unable to tolerate desiccation and temperature.
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.
