Read the following statements carefully and identify correct statements w.r.t. Lichens
a. The association cannot tolerate air pollution, especially due to sulphur dioxide
b. Lichens are annuals and their growth is slow
c. The fungal partner mostly belongs to ascomycetes.
d. Soredia are most efficient means of asexual reproduction
e. Orchids seldom occur without this association
f. Foliose lichens are pioneers of succession in a water body.