[I choose b.]
Why are there so many species still unknown to modern science?
a.many of these species are found in remote environments.
b.smaller species receive less attention than large organisms.
c.Cataloging these species is a huge task
d.all the above
Many have not been discovered, because of the remoteness of the fauna, and because of the very large task it is to cataloge the plants.
answer b is not enough.