The pronoun "I" should be changed to "me" because it is not the subject of the sentence, so the phrase "Jon and I" contains the sentence's error.

This sentence uses the wrong pronoun case. If a first person pronoun is the object of a preposition, it should be “me,” not “I.” The corrected sentence reads, "I was almost to the exit of the building, but standing between me and the doors was a gigantic security guard looking right at me."

"Parents and I" is the object of the preposition "to," so it should instead be "parents and me."

In this sentence, the wrong pronoun case is used. “I” is a subject, but here it appears as the object of a preposition. The corrected sentence reads: My sister took my hand and solemnly swore that nothing would ever come between her and me.

This sentence uses the wrong case of pronoun. As an object, the first person pronoun should always be “me.” The corrected sentence reads, "There was a new person who I had never seen before standing between my sister and me in the line."

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."