"Affective" is easily confused with "effective." "Affective" means to influence someone emotively, while "effective" means to produce a desired result. 

Here, the problem is that the regulations will not be "effective," or produce the desired result. However, the sentence uses the word "affective," which is not the proper word choice. Therefore, "affective" is the part of the sentence that contains an error.

"Its" and "it's" are a pair of homonyms that are often confused. Without the apostrophe, "its" is the possessive form of the pronoun "it." On the other hand, "it's" is the contraction of "it" and "is." In this sentence, "it is no surprise" captures the sentence's meaning, but the possessive form of the pronoun "it" does not make any sense. So, "its" is the part of the sentence that contains the error.

"They're" is a contraction which means "they are." The correct form in this case is the possessive pronoun "their." So, "they're" contains the sentence's error.

"Where" speaks to location. In this sentence, the clause should be "during which" or "in which." Note that '50s is appropriate: it is never "50's."

This sentence uses “that” where “which” is more appropriate. Use “which” for added information, after a comma. The corrected sentence reads, "The last question, which was asked by the town’s famously off-kilter librarian, addressed the completely irrelevant issue of protection against government spying."

This sentence uses the wrong version of there/their. The possessive “their” is appropriate in this case. The corrected sentence reads, "Judging from their aversion to loud noises, I doubt that the cats will enjoy having three toddlers running amok."

“That” would be a better substitute for “which” since the island we’re referring to is a thing. “Which” is used to refer to an action and/or introduce a new clause, especially after a comma. For example, “I couldn’t understand the directions, which bothered me.”

This sentence contains a common usage error—the word "accepted," meaning allowed into, has been confused with the word "excepted," meaning specifically left out. Confusing these words completely changes the meaning of the sentence.

In this sentence, the phrase "had been involved in the hit-and-run from last year" is not a subordinate clause. Rather, it is part of the main clause and helps to identify which truck in particular the speaker is referring to. Because it is not subordinate, the use of the word "which" is inappropriate and confusing. The word "that" should be used instead.

This sentence mixes up the words “that” and “which.” “Which” is used to start a phrase that provides additional information after a comma. The content of a which-phrase is loosely connected to the content of the main phrase, and the sentence would still make sense if the information contained in the phrase were omitted. “That” directly follows the word it’s modifying, with no comma intervening. The corrected sentence reads, "Nancy brought over the most heavenly-smelling batch of pecan rolls, which would have been lovely if I weren’t allergic to both nuts and gluten."