In the example sentence, "if you don't stop smoking" is clearly a dependent clause. Since this dependent clause comes before the main clause, it is acting here as an introductory phrase and must be punctuated with a comma.

Interrupting phrases must be separated from the rest of the sentence with commas. Here, the grammatical subject is "pork," this subject is then described in a grammatically irrelevant, but contextually useful, interrupting phrase. Because it is outside of the basic structure of the sentence, the interrupting phrase "one of my favorite kinds of meat" should have one comma at the beginning and one comma at the end.

In this sentence "Derek Jacobi" acts as an interrupting appositive phrase, and thus must be enclosed with commas. Here, the subject is first identified as "my favorite actor of the previous generation," and is then renamed with a proper noun. The actors name is important information contextually, but is not fundamental to grammatical structure of the sentence, since the grammatical subject remains "my favorite actor of the previous generation."

The underlined portion of the sentence contains just one error. The word "Shortly" is used as an introductory phrase, describing when the action of the sentence took place. Any introductory phrase needs to be set off by a comma. "Shortly, the windows opened" is the best choice to improve the sentence.

Commas, gramatically speaking, should never be used before or after the word "that." The correct sentence would have: "James finally saw the movie that his friends . . ."

"Had recommended" could be changed to "recommended", for the sake of simplicity, but the comma error is more flagrant.

The sentence consists of two independent clauses ("Joey will reluctantly eat broccoli and spinach" and "his favorite green vegetables are peas and green beans") joined by a coordinating conjunction, "but." (Other coordinating conjunctions can include "and," "or," "nor," "yet," "so," and "for.") When two independent clauses are joined by a coordinating conjunction, a comma is required after the first clause immediately before the conjunction. The corrected sentence would read, "Joey will reluctantly eat broccoli and spinach, but his favorite green vegetables are peas and green beans."

“While I would love to go to the beach with you” is a dependent clause, which means that if it is removed from the sentence, the rest of the sentence (“I have to study instead”) will still be a complete sentence. Because commas are always used to separate a dependent clause from an independent clause when the dependent clause precedes the independent clause, a comma must appear between “with you” and “I have.”

“Wherever they go” is a dependent clause, so it must be separated from the rest of the sentence by a comma. However, commas generally don’t appear before or after the word “that,” so no comma is necessary there. (Specifically, commas are not generally needed to separate dependent clauses from independent clauses when the dependent clause follows the independent clause.)

“Being a strong student” is a modifier that describes “Chris,” so a comma is needed to separate the two. The three items in the list are properly punctuated with commas, and since "classmates" is plural, the correct possessive is "classmates’."

Because “Here’s the situation” is an independent clause introducing another independent clause, a colon is the correct punctuation mark to use to separate them. A comma is required after “adults,” though, since it’s an item in a list.