[A]: The secondary pholem consititutes a less poriment part of the tree trunk than the secondry xylem
[R] : The amount of Phloem produced by the cambium is smaller than that of seconday
A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false
