The use of the word "only" is incorrect in this sentence, as the second part of the sentence makes it clear that the subjects read "only" the individual's author's work. The sentence is written to make it seem like the subjects are the only people reading the author's work. "They read only the author's books" is the answer choice that best fixes the problem.

The insertion of the adverb "rarely" after "had" makes its usage confusing and unclear, since the reader is not sure which verb it is modifying. By placing "rarely" between "has" and "had," the meaning of the sentence becomes clearer, and thus the correct answer is "Currency has rarely had any uniform shape or design throughout human history."

The placement of "only" in the sentence makes the sentence confusing, as it seems as if the subject were "only" one of many "third drivers" "to win ten races in one season," which doesn't make sense. The sentence only makes sense if it suggests that the driver in question was just "the third driver" ever to achieve the feat. The answer choice that correctly deploys "only" is, "He was only the third driver to win ten races in one season."

The insertion of "only" between "is" and "the" makes it unclear what the word is modifying in the sentence. As "only" is modifying "way," it should be placed next to it in the sentence; therefore, the correct answer choice is "Widespread structural reform is the only way the organization can remain solvent in the future."

The word "arguably" is an odd place in the sentence that makes it unclear exactly what is being modified by the word. As the thing that is arguable is the status of "the Zulu tribe" against other British opponents. Therefore, the clearest and best answer choice is "was arguably the British army's most formidable opponent."

With "anywhere" placed after "practicing," the sentence reads as though the problem was in "practicing anywhere" rather than its intended meaning of finding something "anywhere" on which the racers could practice. The answer choice that best clarifies this is "like it anywhere for practicing."

The use of "only" at the very beginning of the sentence creates confusion throughout the rest of the sentence. As it needs to directly modify "cure," it should be moved directly next to it. The answer choice that appropriately does this is "The only cure for the common cold is rest, relaxation, and fluids."

The main issue with the underlined phrase is one of word order, as "before" is stuck in a place that makes the meaning confusing. To improve this phrase, "before" should be moved to work with "never." "Such actions had never before been undertaken," is the correct answer choice.

The placement of "only" in the sentence is confusing, as it is unclear what "only" is modifying. By moving "only" after the verb, it makes it clear that "only" modifies "able," making the correct answer "The tickets were only able to be given out to people who called the radio station."

The word "fewer" is in a strange and confusing place in the sentence. The sentence needs to be restrutured so that the veterans have "fewer" "in number." Therefore, the correct answer choice is "the veterans of the war grew fewer in number."