The verb tenses in this sentence do not work together. The first part of the sentence takes place before a point in the past (when Harrison solved the problem), so the correct verb would be “had not been able.” The corrected sentence reads, "Seafarers had not been able to measure longitude during their journeys until the 18th century, when clockmaker William Harrison solved the problem with a very precise clock."

There is no reason for the last verb in this sentence to be in the past progressive tense—it happened at a singular point in the past. The corrected sentence reads, "Frustrated by the limited career options in his small, rural hometown, Frank ran away with the circus and became a contortionist."

This sentence uses the wrong form of the verb “to be.” After “found,” it is correct to use the infinitive "to be" instead of "being." The corrected sentence reads, "Although he found his job to be dreadfully boring, he remained committed, knowing that his wages would buy him a plane ticket to Paris."

The timeline of this sentence is off. The first phrase is in the past tense, so the verb “has taught” needs to indicate that it happened before that point in the past. So, "has taught" should be changed to "had taught," and "has taught" contains the sentence's error. The corrected sentence reads, "Long before she began her tenure as chair of the Biology department, Professor Green had taught undergraduate classes in Spanish literature."

This sentence describes a situation that did not happen, and should use the conditional “would” instead of the future tense “will.” The corrected sentence reads, "The show would not have been such a fiasco if the animals had not escaped from their kennels just as the curtain was rising."

This sentence uses the wrong form of the verb “to find.” In order to fit into the timeline of the sentence, it should read “having found” or possibly "finding." The corrected sentence reads, "Her flat intonation masked the incredible excitement she felt at having found the prize in the cereal box."

This sentence uses the "-ing" verb “being” when it isn’t necessary. In fact, this sentence is a fragment as it is written, but can be made into a complete sentence by changing "being" as "is." This also sounds much cleaner and more direct. The corrected sentence reads, "The issue is that the director does not come into the office on Fridays and I am not familiar with the process she uses."

The gerund “being” here is unnecessary and makes the sentence sound clunky. Replace it with “was” to make the sentence run more smoothly: "Robert was always the top of his class in high school, and he put enormous pressure on himself to maintain his rank in college."

The entire sentence refers to the past, as we can tell from the verb "was" in "who was unusually intelligent" and the verb "was" in "was able to play." Therefore, the verb "sees" should be in the past tense like the rest of the verbs in the sentence. To correct the sentence's error, we would need to change "sees" to "saw."

"Lead" is in the present tense. Given that the rest of the sentence is in the past tense, this verb should also be in the past tense. Therefore, it should be "led," not "lead."