Assertion: Herbivores are also called as key industry animals because they convert plant matter into animal matter.
Reason: Decomposers play a pivotal role in the ecosystem and they indirectly suppor the producers.

Answer

B

Explanation

According to Elton (1939), herbivorous animals are key industry animals as they convert plant matter into animal matter and all other consumers' (higher animals') lives are dependent upon these primary consumers.
Decomposers (also called as transformers) transform organic compounds into simple inorganic compounds. Saprophytic fungi and bacteria belong to this category. They act upon dead bodies of plants and animals and decompose them to their elemental stage. These in turn can be used by producers for their growth and photosynthetic activity. In this way, decomposers indirectly support the producers and play a pivotal role in ecosystem.