This sentence contains no errors. The sentence contains two independent clauses that are not joined with a conjunction, so the appropriate punctuation here is a semicolon. The correct choice is "singing for years; he even was part of many well known choirs."

This sentence contains no errors. The phrases "Every other week" and "to him" are examples of introductory phrases, 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.

"Even the garage" is 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 should also be introduced and completed with a comma in order to separate them from the main clause of the sentence.

Furthermore, the sentence combined two related independent clauses together without the use of a coordinate conjunction. When this is the case, a semicolon should appear between them, as it does after the word "garage" in this sentence. 

The correct choice is "Every other week, he would spend the day cleaning the entire house, even the garage; to him, it was a form of meditation as well as basic housekeeping."

This sentence contains no errors. The colon after "stated" is appropriate because the following clause, the quote, explains what the book stated. Double quotations should be used because this is a direct quote/saying from the book. Within the quote itself, the phrase "I am one of the few honest people that I have ever known" also explains the clause preceding it, so the colon before the word "I" is also appropriate. No changes are necessary. The correct choice is " The book stated that: "Everyone suspects himself of at least one of the cardinal virtues, and this is mine: I am one of the few honest people that I have ever known." "

This sentence contains no errors. The phrase "Because the programmer forgot to add a word into his code" 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. It is perfectly acceptable for the word "because" to start the sentence, as long as the sentence is punctuated correctly. Note, however, that "The entire program did not work, because the programmer forgot to add a word into his code" is incorrect because a comma should not appear before the word because in the midst of a sentence. The correct choice is, "Because the programmer forgot to add a word into his code, the entire program did not work."

This sentence contains no errors. No additional punctuation, such as commas, are unnecessary because there is not a separate clause in this sentence. The word "as" here acts as a preposition (as well as "from"), and prepositional phrases are not separate clauses. The correct choice is, "every weekend as a way to unwind from a stressful week."

This sentence contains no errors. The phrase "Unbeknownst to many people" 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 word "as" acts as a preposition in this sentence, so a comma preceeding the word is unncessary. Lastly, while it is common to spell numbers less than 10, it is best that the "two" and "one hundred" are both spelled out for the sake of consistency (not to mention, in one choice, "$100 dollar" is redundant).

The correct choice is, "Unbeknownst to many people, the United States used to print two dollar bills as well as many bills much larger than the one hundred dollar bill."

This sentence contains no errors. The words "to" and "after" both start prepositional phrases, meaning that they are a part of the main clause as well. No additional punctuation is necessary: commas are used to separate clauses (there is only one) and colons combine clauses when the second one explains or clarifies the first (again, only one clause). The correct choice is, "He planned to retire to the mountains after this year."

This sentence contains no errors: it is a simple sentence. Note that prepositions (e.g. "since") do not mark the beginning of a new clause, but simply a prepositional phrase - they are still considered a part of the same clause as the words preceding it. Additionally, commas are generally used to separate clauses (as stated before, there is only one clause). No changes should be made. The correct choice is, "She has played the guitar ever since she was very little."

This sentence contains no errors. The sentence combines two related independent clauses without the use of a conjunction, so a semicolon is appropriate after the word "poetry." Additionally, "though his poems were short and sweet" 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 choice is, "himself in his poetry; though his poems were short and sweet, they contained much gravitas."

This sentence contains no errors. The words "large" and "strong" are coordinate adjectives describing the word "foundation." These adjectives modify the same noun separately, but are not separated with a conjunction. Coordinate adjectives need to be separated with a comma. The correct answer choice is, "The large, strong foundation was necessary for a building."