In the sentence, the phrase "unaware of the historical circumstances" is an interrupting phrase, or a phrase that provides information but is not a necessary component of the complete sentence. Such clauses always need to be set apart from the rest of the sentence by commas. Thus, "Many Americans, unaware of the historical circumstances," is the correct answer choice.

The phrase "the band's lead singer" is an appositive phrase; it renames the subject (here, "Francine") and provides additional information about the subject. In this case, the phrase "the band's lead singer" could be removed from the sentence without changing its meaning, so it needs to be surrounded by commas.

The phrase "as disputatious as ever" is a non-restrictive interrupting phrase, or a phrase that provides extra information and is not necessary to the meaning of the sentence. Any such phrase must be set apart from the rest of the sentence by commas. As such, "The boys in the band, as disputatious as ever," is the correct answer.

The word "Frequently" in the sentence is used as an adverb describing the actions of the students; therefore, it must be set apart from the rest of the sentence, and "students" in particular, to work as an introductory phrase. "Frequently, students" is the correct answer.

The phrase "day by day" is used in the sentence as an introductory phrase, modifying the meaning of the sentence. As such, it needs to be set off from the rest of the sentence. "Day by day, fewer" is the correct answer choice.

The phrase "when researching employment opportunites" operates in the sentence as an introductory conditional phrase, giving a necessary "if" to the sentence. Such a clause needs to be appropriately set apart from the rest of the sentence; therefore, "employment opportunities, college students" is the correct answer choice.

The word "everyday" in the sentence acts as a conditional phrase, indicating how often people do what is described in the sentence. Such a phrase, must be set off by a comma from the rest of the sentence. Therefore, "Everyday, people" is the correct answer choice.

The underlined portion of the sentence contains a slight punctuation error. Speciifically, the word "Lately" is used as an introductory phrase, explaining the condition under which the action takes place, and such clauses need to be set off by a comma from the rest of the sentence. "Lately, families" is the correct answer.

The phrase "On this date" is an introductory clause, describing when the action of the sentence took place. An introductory clause must be set apart from the rest of the sentence by a comma. Therefore, "On this date, an unspeakable evil" is the correct answer choice.

The phrase "Unfamiliar to most listeners" is used in this sentence as an introductory phrase, something that explains the actions of the rest of the sentence. All such sentences must be set apart from the rest of the sentence by a comma. "Unfamiliar to most listeners, the band" is the correct answer.