Why did the five-kingdom system of classification fall out of favor?
a. there were too few monerans to justify their classification at the kingdom level.
b. it did not reflect the actual evolutionary relationships among organisms very well.
c. it was too complex - the original two-kingdom system of linnaeus was more useful.
d. it was too difficult to distinguish plants from fungi and animals from protistans.

Answer is B. It did not reflect the actual evolutionary relationships among organisms very well.

Explanation:

The five-kingdom system of classification was initiated or formed by Robert H. Whittaker in 1969. And it involved the Kingdoms monera, fungi, protista, animalia and plantae.

This classification system was regarded as not so good because of placement of some certain organisms. For example, in the classification system, unicellular algae were put under the kingdom protista, when other multicellular organisms like algae were being classified under the kingdom Plantae.