This sentence contains no errors. It joins two independent sentences without the use of a coordinate conjunction, so a semicolon should be present after "horizon." Furthermore, the phrase "especially with the invents of Google's car and various competitions" 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. The correct answer choice is, "It seems like the age of driverless cars are on the horizon; especially with the advent of Google's car and various competitions, the average person may be able to afford one within the next few decades."

This sentence does not contain any errors. This sentence combines two independent clauses without the use of a coordinate conjunction, so there should be a semicolon before the word "it." No colon is needed after "than." The correct choice is, "Russia is well known for its natural gas resources; it produces more than 10% of all the world's gas."

This sentence contains no errors. The phrase "such as Elon Musk" is functioning as a parenthetical expression to give an example of one of the people working to the end of "consumer space travel," so it should be surrounded by commas. While this phrase could also function as a normal part of the main clause (thus, eliminating the need for commas), that is not an option available in the choices. The correct answer is, "People, such as Elon Musk, are working in order to make consumer space travel a reality."

There are no errors in the above sentence. This sentence joins two related independent clauses without the use of a coordinate conjunction, so there should be a semicolon present after the word "time." In the other sentences, there are issues with parallelism (found...finds), verb agreement (loved to plays), word errors (freetime is not one word), or using a comma where a semicolon should be used. The correct choice is, "Christopher loved to play video games in his free time; he found playing them relaxing."

There are no errors in this sentence. There is no need for additional punctuation. The word "because" is appropriate because it acts to join the two clauses and show a cause and effect. The words "but" and "and" do not do this and are therefore inappropriate. The correct answer is, "Naomi was learning to play the guitar because she liked the sound of the instrument."

There are no errors in this sentence. The use of quotation marks is appropriate because the word "reading" is being used in an usual way in that it does not actually refer to what most people would call reading. The comma is necessary after "reading" because the phrase "When he said he was 'reading' " is an example of an introductory phrase. It explains information necessary to the context of the sentence, but is 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. The correct answer choice is, "When he said he was "reading," he was actually referring to listening to audiobooks."

This sentence contains no errors. The sentence joins two related independent clauses without the use of a coordinate conjunction, so a semicolon should appear after the word "remarkable." The other sentences contain errors in voice (Using "was considered"), punctuation (Using a comma where a semicolon is needed), or tense (The use of "collected" instead of "she began collecting"). The correct choice is, "Many considered Helen's collection remarkable; she began collecting when she was very young."

This sentence contains no errors. It is a simple sentence, so no punctuation is necessary. The correct choice is, "Advertisers must compete in order to get in front of viewers." All of the other sentences misuse punctuation, except for one, which has a voice error ("are challenged").

This sentence contains no errors. The sentence combines two independent clauses without the use of a coordinating conjunction, so a semicolon is appropriate after the word "parent." Additionally, the phrase "while some people prefer to be very hands-on with their children" is an example of an introductory phrase, which explains 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. The correct answer choice is, "what makes the ideal parent; while some people prefer to guide their children throughout their development, others prefer."

There are no errors in this sentence. The phrase "In the past few decades" 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. No additional punctuation is needed. The correct choice is, "In the past few decades, workplaces have been moving to a more collaborative model."