This sentence uses the wrong pronoun. The word "which" is never used for nouns which refer to humans. The correct choice here is "who." No other changes are necessary. Note that "that" does not begin a relative clause (in which case you would have to omit the commas), and the word "being" generally has to do with existence and is never used in this way. The correct choice is, "the teens, who were excited, bought much food."

This sentence misuses the word "which." Since the sentence is about the Presidents (this is the subject), "which" is inappropriate as it can only refer to non-humans (Additionally, nations cannot "convene," but representatives (i.e. people) from those nations can). If the relative clause were to be re-written, it would be "they convened to talk about world issues." Since "they" is acting as the subject here, the correct word to replace it would be "who." The correct choice is, "who."

This sentence misuses the word "it's." This form of the word "it" is a contraction for "it is." Since the word is meant to be possessive here, the correct form is "its," containing no apostrophe. No other changes are necessary. The correct choice is, "for the success or failure of its products."

This sentence misuses the word "its," which is the possessive form of the word "it." It is clear from context, however, that the contraction, "it's" is necessary here. The correct choice is, "It's important to study every day." The other choices do not contain legitimate forms of the word "it."

You can immediately cross out the answer choice with a gross error in both mechanics and grammar: "whos'". Using the relative pronoun "that" to describe a person is incorrect. In this case, the relationship between the noun "man" and the "dog" is one of ownership. We need to use the possessive relative pronoun "whose". All of the other answer choices incorrectly address these two points.

The central issue here is not verb tense usage but, rather, incorrect pronoun usage. "Who's" represents the contraction of the pronoun and verb "who is." The correct possessive form of the pronoun who is "whose." All of the other answer choices do not address this issue.

The correct answer will resolve the redundant relative pronoun that, replacing it with the definite article "the". Using the article "a" is problematic precisely because the article refers to a definite noun "the number of people...". The other answer choice that attempt to implement a subordinating conjunction all result in issues with awkward syntax.

This sentence misuses the word "who's," which is a contraction for "who is." The context of this sentence dictates that the possessive form of the word be used here. The correct choice is "whose." The other choices are not actual forms of this word.

This sentence misuses the pronoun "his." Since a man is not mentioned anywhere in the sentence, it makes no sense to use the word "his." Most likely, it is Sharon's project that is meant here, meaning that "her" should be used. Note that "hers" is not a proper word. The correct choice is "her."

This sentence contains an error in the usage of "it's," which is a contraction for "it is." The context of the sentence makes it clear that the possessive pronoun is needed here, which is "its," without the apostrophe. Note that "that" is not specific enough (could be referring so some other battery), and "the car's/of the car" is redundant, given the first half of this sentence. The correct choice is, "he tried changing its battery."