A biological reserve that is designed for a single species is an important tool in maintaining biodiversity because a reserve:.
a) that is designed to protect a species will always be maintained as a reserve.
b) will generate income when people visit to see the biodiversity protected in the reserve.
c) will not change over time so all the species will be conserved as long as the reserve exists.
d) that is designed for a single species will also protect other species in the reserve.

Explanation:

Biological reserves also known as natural reserves, and plays very important role in protecting genetic diversity.

Biological reserves are multipurpose protected areas with boundaries restricted by laws.

They have various goals; but the main goal of biosphere reserve is to preserve genetic diversity by protecting wild animals as like in their natural areas, and domesticated plant or animal genetic resources and many others goals too.

A terrestrial biosphere reserve consists  different zones;  zone of core, buffer and transition zone.

A biological reserve that is designed for a single species will also protect other species in the reserve.

the answer to your question is b