"Have led" refers to "the order of operations," or more specifically, "order," a singular noun. "Have" is a verb that is used with plural nouns, so it does not agree with the singular "order." To fix the sentence, "have" would need to be changed to "has."

"Dinosaurs" is in its plural form, and needs to be accompanied by a verb also in the plural form. Thus, "is a" contains the sentence's error, and should be changed to "are."

In this sentence, the plural pronoun “their” does not agree with its singular antecedent, “the woolly mammoth.” The corrected sentence reads, "The woolly mammoth, a relative of the elephant, roamed through northern Eurasia and North America before its extinction."

In this sentence, the pronoun “they” does not agree in number with its singular antecedent, “the ruby-tailed tree crawler.” The corrected sentence reads, "The ruby-tailed tree crawler is a rare species of caterpillar; it only lives in isolated sections of the Amazon jungle."

This sentence has a pronoun that does not agree with its antecedent. “It” is singular, but it refers to the plural “chickens” and “dinosaurs.” The corrected sentence reads, "Modern-day chickens did not evolve from prehistoric dinosaurs, but they do share a common ancestor."

The first part of the sentence introduces the spider as a singular noun. The second part, where the sentence uses pronouns, should match this by referring to the spider using singular pronouns. The corrected sentence reads, "The tree-toothed spider is migrating north from the Amazon, where it made its home previously."

This sentence contains an error in pronoun case. "Her father and her" is incorrect because "her" is an objective pronoun, whereas a subjective pronoun is needed because Amy performed the action "had built," along with "her father." If you find it hard to see why the sentence's use of "her" is incorrect, try taking out the phrase "her father and"; you wouldn't say "Little Amy beamed proudly as she described every detail of the model rocket her had built." So, "her father and her" is the part of the sentence that contains an error.

This sentence uses the pronoun “yourself,” even though it is talking about “people living in cold and snowy climates” in the third person. One way to correct this is, "For people living in extremely cold climates, putting on warm mittens and boots just to cross the street is a necessary precaution for protection from the cold."

This sentence uses the relative pronoun “which” to describe people. The personal version “who” is better: "Contrary to popular belief, the most dangerous pirates were often the ones who had two wooden legs."

The word, "doctor" is singular. Therefore, pronouns that refer back to the doctor should also be singular. "They" is plural and therefore is incorrect; the phrase "he or she" should be used in the sentence, as we do not know the doctor's gender.