The timeline of the verb tenses in this sentence is slightly off. The corrected sentence reads: Since the argument about cheese curds, Paul and I have not been speaking to each other more than is absolutely necessary.

The underlined portion of the sentence is a conditional phrase, explaining the condition under which "the police stood watch." As such, the verb in the phrase needs to actually be a gerund, or a verb describing action that functions as a noun; therefore, "Allowing the students to continue their protest," is the correct answer choice.

The sentence is written in the present tense, except for the modal verb, "could," which expresses possibility where none is needed; we're told that John "always" orders basic dishes. "Could" should be changed to the present tense verb "can" so that its tense matches that of "orders."

Since the speaker is talking about a hypothetical situation, it is appropriate to use the subjunctive mood to denote that. The sentence should therefore begin "If I were the principal," ("were" being the first-person subjunctive form of "is") rather than "If I was the principal."  Look out for key words such as "if" or "I wish" to denote where the subjunctive mood should be used.

Since the speaker of the sentence is discussing a hypothetical situation, the verb "was" should be changed to its subjunctive form, "were."

In this sentence, the writer is referring to a hypothetical situation of Caleb being in charge. This requires the use of the subjunctive mood of the verb. The phrase "if he was in charge" should therefore be changed to "if he were in charge," so "was" should be replaced with "were."

The sentence is written entirely in present tense without the use of modal verbs except for the modal verb "could." In order to maintain consistency, we need to change "could" to "can."

In this sentence, Patrick is describing a hypothetical situation in which he is in charge of the house. Since this situation has not actually happened, he would need to use the subjunctive mood for the "verb" is and change "was" to "were" ("if he were in charge").

While the majority of the sentence is written in the present tense, the modal verb "could" expresses potential unnecessarily. "Could" should be changed to the present tense "can" in order to match the mood of the sentence. 

"If I were" is correct because subjunctive mood is needed in hypotheticals introduced by "if." "Were" is correct here, not "was." A comma is appropriate between "restaurant" and "I" because an introductory phrase should be separated from the rest of the sentence by a comma. "Would be" is consistent with the mood of the sentence, and there are no issues with "ingredients and combinations." There is no error in the sentence.