You a Given a Plant Tissue in Lab and Asked

You a given a plant tissue in lab and asked to determine if the tissue is a source or a sink. Microscopic analysis reveals an abundance of colorless parenchyma cells with plastids. Only one biochemical test reacts positively with your sample. In the presence of iodine, the plastids turn a dark purplish color. Based on this information you determine your sample is

A) a source because your sample is rich in carbohydrates.
B) a source because your sample contains plastids.
C) a sink because your sample is rich in carbohydrates.
D) both a source and sink because it contains both plastids and carbohydrates.