which of the following is not a decomposer?
(a) yeast
(b) mushroom
(c) bread mould
(d) lichens

Dear student,

All of the mentioned options are well established  examples of decomposers. Yeast, bread moulds, and mushrooms are fungi where as lichens are formed by a symbiotic relationship between algae and fungi (dominant partner). They are all capable of breaking down dead and decaying organisms into simple inorganic material.

Regards,