This sentence contains no errors. It is a simple sentence, so no punctuation is needed whatsoever. Note that the choice that rewords the sentence is grammatically correct, but it is not the clearest or most precise since it replaces the active voice with the passive voice unnecessarily. The correct choice is, "Learning a new language requires many hours of practice."

There are no errors in this sentence. Having a " 's" after each of the individuals' names is appropriate because it shows individual ownership; Hank and Julie do not own the same pets, but their own pets respectively. The correct choice is, "Hank's and Julie's pets caused much trouble around the neighborhood." All other choices change the meaning of the original sentence. While "their" is a possible substitute for "Hank's and Julie's," it is more ambiguous as it implies that they own the same pets when that is not the case. 

This sentence does not contain any errors. It is a simple sentence and is correct as is. The words "absolutely," "differently," and "seemingly" are adverbs, so they do not need to be separated from the other words (verbs or adjectives) with commas. Punctuation of any sort would be inappropriate and would result in an awkward sentence. The correct choice is, "Cole was absolutely fascinated by the ways some materials would react differently under seemingly similar conditions."

There are no errors in this sentence. The underlined portion is one cohesive clause, so no punctuation is necessary. Specifically, a comma should not come before the "and," since the conjunction is not being used to join two independent clauses. Commas should only appear before a coordinate conjunction when the conjunction joins two independent clauses. The correct choice is, "Some experts believe that countries will engage in physical warfare less in the future and engage in more subversive acts of aggression." 

This sentence does not contain any errors. Commas do not appear before the word because when it joins clauses and no changes are needed in general. A semicolon at the end of this clause is also inappropriate because the following clause is not an independent one. The correct choice is, "Duke preferred to listen to audiobooks in stead of reading because he could do other things while listening to them."

There are no errors in this sentence. The phrase "While many people find abstract art strange and confusing" is an introductory phrase, explaining information necessary to the context of the sentence, but outside of the main sentence, grammatically. These types of phrases must be followed by a comma in order to separate them from the rest of the sentence. No additional punctuation or changes are necessary. The other sentences contain errors in voice, punctuation, and tense shift. The correct choice is, "While many people find abstract art strange and confusing, Leah finds most abstract art to be calming."

There are no errors in this sentence. This sentence joins two related independent clauses without the use of a coordinate conjunction; therefore, a semicolon is necessary before the word "she." No additional punctuation is needed. Note that in order to use a comma, a conjunction would need to be present, and a colon is inappropriate because, while related, the second clause does not actually clarify or explain anything about the first clause: it gives additional information. The correct choice is, "Macy always loved to learn new words; she often spent her free time looking up words in the dictionary."

There are no errors in this sentence. The sentence is a simple sentence, so no punctuation is needed. Specifically, the hyphen between "board" and "game" in one of the choices is unnecessary because it does not add any clarity to the sentence as a whole. The best choice is, "Chess is the most popular board game in the world."

There are no errors in this sentence. The phrase "When he sang" is an example of an introductory phrase, explaining information necessary to the context of the sentence, but outside of the main sentence, grammatically. These types of phrases must be followed by a comma in order to separate them from the rest of the sentence. Additionally, the phrase "paired with the sweet melody of the song" is an example of a parenthetical expression: a phrase that explains more about a particular word or phrase in the sentence, but is not introduced by a relative pronoun. These phrases must be introduced and completed with a comma in order to separate them from the main clause of the sentence. The correct choice is, "When he sang, his voice, paired with the sweet melody of the song, brought many people to tears."

There are no errors in this sentence. This is a simple sentence that happens to have a compound predicate (last half of the sentence). No comma is necessary before and in order to join two halves of the same clause (only use the comma when joining two independent clauses). Furthermore, it is rare to put punctuation between a preposition and its object, unless you are making an interjection within the prepositional phrase. This is not the case, so no punctuation is needed whatsoever. The correct choice is, " for his genius and personality."