There should not be a comma between the words “skateboarding” and “and.” In other words, the second part of the sentence should read “including skateboarding and playing video games.” This is because there are only two interests listed. A comma should only be used in lists containing three or more items.

Since the list "full, happy, and tired" has more than 2 items, each item before the last item must be separated using a comma. Inserting a comma after "happy" will make this sentence correct, so the underlined phrase "happy and" must be changed. Note that a semicolon is correctly used to separate two independent clauses from one another in this sentence.

Since the names Yolanda and Sam are the only items in the list, they do not need to be separated by a comma. We use the conjunction "and" to combine items in a two-item list, so "Yolanda, Sam" should be changed to "Yolanda and Sam." If Yolanda and Sam had a third friend, named, say, Suzannah, then commas would be needed to separate each name in the list.

Here, "finally" is considered an introductory word, so it must be followed by a comma: "Finally, the teacher . . ."

The phrase "If you decide to go to the beach" is an introductory phrase, and all introductory phrases need to be set apart from the rest of the sentence by a comma. So, after being corrected, the sentence would read, "If you decide to go to the beach, make sure to wear sunscreen to protect your skin!"

Because the sentence states that Margot is not Daisy's only sister, the commas and which frame her name in "their numerous older and younger sisters, Margot, and Daisy" are incorrect. The comma that sets apart Margot's name at the beginning of the sentence ("Daisy and her sister, Margot, shared") is correctly used, because here, Margot is being specified as Daisy's sister in an appositive phrase that renames "her sister" as "Margot."

"The treasurer" here is an appositive: it renames or restates Shindra in different words, and it should be surrounded with commas. The correct sentence should be: "the students voted Shindra, the treasurer, president . . ."

Here "despite being an old city" needs to be separated by the main clause by two commas, not just one.

The word "however" here is considered a non-essential phrase: it can be removed, leaving a complete sentence. So it must be surrounded with commas: "The project leader, however, continued . . ."

Commas should be used to set off the phrase "the lost princess," as it is in apposition to (gives a description of) the subject Perdita, but the sentence still makes sense without it. So, "Perdita the lost princess," contains the sentence's error, and the sentence should read, "Perdita, the lost princess, was found and raised by a shepherd."