Disclosure: Taken from Knewton Quiz solution.
ExplanationThis sentence displays a special kind of pronoun-antecedent agreement error. Describing
kingdom Eubacteria as one of something means that the entity that the singular
kingdom is
one of must be plural.
Think about simpler cases: "This program is one of my favorite
shows," NOT "This program is one of my favorite
show."
Kingdom Eubacteria is the only one of...the classification system (a singular noun) is incorrect.
Additionally, the original construction uses the pronoun who, which is used to refer to a person, to describe the
kingdom Eubacteria.
Choice C uses a simpler and grammatically correct construction to express the same idea.
Kingdom Eubacteria, a singular noun, agrees with the singular verb
displays.
Alone among is an idiomatically correct expression.
That comprise the classification system is an adjective clause immediately following the noun it describes,
the six kingdoms.
The correct answer is C.Choice B retains the "singular item out of a singular entity" error. Additionally,
they is used to refer to a singular pronoun,
kingdom Eubacteria.
Choice D uses the plural are to describe a singular noun,
kingdom Eubacteria.
In displaying is an awkward and unclear prepositional phrase.
Choice E retains the singular item out of a singular entity error. Additionally,
only of is an idiomatically incorrect, unclear, and awkward way of expressing one item out of several items; this expression would mean a number of things:
the shirt only of (made of) wool.