The sentence is written as a compound sentence, containing two complete independent clauses, but does not properly connect them. A compound sentence must be connected either by a semicolon or a comma and conjunction, which in this sentence is "because." Therefore, the correct answer choice is "Home cooks are at a disadvantage to professional chefs, because the quality of their equipment is not at the same level."

The phrase "as it was all they had to eat" is used as an explanatory phrase, which is unnecessary to the construction of the sentence. Such a phrase needs to be set apart from the rest of the sentence by a comma; therefore, the correct answer is "the poor meat, as it was all they had to eat."

The phrase "preferring to use simplifying language" is a dependent clause, a clause that cannot be used as a complete sentence but instead relies on other information. Although it cannot stand alone, it still needs to be separated from the rest of the sentence by a comma; therefore, the correct answer is " displays of his verbal acuity, preferring to use simplified language."

The only problem with the sentence is that it is a compound sentence, shoved into a run on sentence. The sentence consists of two complete thoughts, joined by the conjunction "which." All such sentences must be divided by a comma before the conjunction, making "than the youngest kid, which allowed him" the correct answer choice.

A comma is not needed between independent and dependent clauses when the independent clause comes first: "The President initially vetoed the bill in order . . ."

The phrase "with the only exception being Fridays" is a dependent clause, and needs to be clearly distinguished from the main clause of the sentence. The best way to do this is by setting a comma between the two parts. The only answer choice that correctly places a comma in the sentence is "He typically worked late, with the only exception being Fridays."

The phrase "despite having none to conduct" is a dependent clause, a clause that cannot stand as a complete sentence on its own, but provides extra explanation to the body of the sentence. A dependent clause always needs to be set apart from the rest of the sentence by a comma. The only answer choice that does this is "The former bandleader still dreamed about conducting an ensemble despite having none to conduct."

The phrase "which stressed their underlings" is a dependent clause, or a clause that relies on the main body of the sentence for its full meaning. Any dependent clause must be set apart from the main body of the sentence by a comma. The answer choice that appropriately uses such a comma is "The managers decided to make a change for no particular reason, which stressed their underlings."

The phrase underlined at the end of the sentence is one whole and complete phrase. Thus, the use of a comma anywhere in the phrase is grammatically incorrect. "Speculation by scholars" is the correct answer choice.

Use a comma to separate the introductory phrase "In many thrilling mystery novels" from the independent clause that in this case makes up the rest of the sentence, "the good guy actually turns out to be the bad guy."