In the sentence, the phrase "a mercenary from a foreign country" is an interrupting phrase, one that provides information but is not critical to the structure of the sentence. All such phrases need to be set apart from the sentence by a comma; therefore, the correct answer is "The soldier, a mercenary from a foreign country, was."

The phrase "tired from their long march" is a non-restrictive interrupting phrase, a phrase the provides information, but is not necessary in the sentence. Such phrases always must be set off by commas. Therefore, "The soldiers, tired from their long march, gladly settled" is the correct answer choice.

The phrase "Under the old regime" is what is called a conditional phrase, as it gives the conditions which make the main body of the sentence possible. Such phrases always need to be set off from the main part of the sentence by a comma; therefore, "Under the old regime, the action was," is the correct answer choice.

The underlined portion of the sentence contains an interrupting phrase, "prone to overly assertive maneuvers." All interrupting phrases must be set apart by commas from the rest of the sentence. Therefore, the correct answer is, "The general, prone to overly assertive maneuvers,."

The phrase "a shrewd negotiator" is an interrupting phrase, a phrase that has no bearing on the construction of the sentence but provides additional information. All interrupting phrases must be set apart by commas; therefore, the correct answer choice is "The executive, a shrewd negotiator, always."

The phrase "anxious about their grades" is an interrupting phrase, or one that provides extra information, but is not crucial to the structure of the sentence. All interrupting phrases need to be set apart from the rest of the sentence by commas. The only answer choice that does this is "The students, anxious about their grades, were."

The list that forms the subject of the sentence, "Angles, Jutes, and Saxons," appropriately separates its items with commas. The comma between "Saxons" and "were" splits the subject of the sentence from the verb, and should be removed. This makes "Angles, Jutes, and Saxons were" the correct answer choice.

The list of names that forms the subject of the sentence is written incorrectly. All lists need to have commas separating their parts from each other for purposes of clarity. The correct answer choice is "Jane, Sally, and Suzy all went to the zoo together."

The list of names that make up the subjects of the sentence all need to be appropriately punctuated. Any such list needs have all the elements set apart from each other; therefore, "Tom, Dick, and Harry have all seen" is the correct answer.

The list that functions as the subject of the sentence needs to have commas separating its elements, distinguishing the different parts. The only answer choice that does this is "Politicians, organizers, and reformers all came together," making it the correct answer choice.