[A]: Long distance flow of photoassimilates in plants occur through sieve tubes.
[R]: Mature sieve tubes have parietal cyto- plasm & perforated sieve plates
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