Lichens Are Vulnerable to Air Pollution Because They Are Unable

Lichens are vulnerable to air pollution because they are unable to excrete toxic substances.They may be prone to taking up these substances because of the

A) presence of algal cells in the uppermost layer of the lichen thallus.
B) preference of lichens for growth on tree bark.
C) high surface area-to-volume ratio of the fungal hyphae composing the lichen.
D) sticky outer surface of the lichen thallus, to which airborne particles become attached.
E) high carbohydrate content, which also makes lichens widely useful as a food source.