On the basis of symptoms of chlorosis in leaves a student inferred that this was due to deficiency of nitrogen.This inference could be corrected only if we assume that yellowing of leaves appeared first in

Question

$\begin{array}{1 1}(A)\;\text{Old leaves}\\(B)\;\text{Young leaves}\\(C)\;\text{Young leaves followed by mature leaves}\\(D)\;\text{Mature leaves followed by young leaves}\end{array} $