(A) : Polar region is not a suitable habitat for small humming birds.
(R) : They tend to loose body heat very fast when it is cold outside.
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.