48. Iron deficiency is often indicated by yellowing in newly formed leaves. This suggests that iron ______.
(A) is a relatively immobile nutrient in plants
(B) is concentrated in the xylem of older leaves
(C) is tied up in formed chlorophyll molecules
(D) is concentrated in the phloem of older leaves
(E) is found in leghemoglobin and reduces the amount available to new plant parts