The forms of verbs used in a list need to agree for the sentence to use proper parallelism. Because the sentence begins its list of two items with "creating," "reduce" should be changed to "reducing" in order to match the form of "creating." So, the corrected sentence would read, "Important things to remember when adding fractions include creating a common denominator and reducing."

The elements in the list should have a parallel grammatical structure. Since the first two use infinitive verbs ("to catch . . . build"), the third should too. The corrected sentence reads, "The final three challenges in the obstacle course were to catch a rabbit, build it an enclosure, and leap over the structure."

The three elements in the list should be formatted in the same way. Since the first two are just nouns without verbals, the third should be too. The corrected sentence reads, "The evening's entertainment consisted of a jazz quartet, a juggler, and a game of musical chairs."

When phrases are enumerated in a list, it is important that the list use parallel structure—that is, it is important that all of the items in the list are presented in the same grammatical form. Here, two of the phrases use gerunds: "dicing" and "baking." We can't change those because they are not underlined, so the phrase "how to spice" should instead be changed to the gerund "spicing."

This sentence contains an error in parallel structure because it does not phrase all of the items in its list consistently. The first two items in the list are nouns ("dexterity" and "precision"), but the third item in the list is a gerund phrase ("being patient"). You could correct this error by replacing "being patient" with "patience."

This sentence lacks parallel structure; the elements in its list should be formatted in the same way. Here, the third element in the sentence's list, "the door was locked," uses passive voice, describing what was done to the door, not what Alice did. On the other hand, the first two items in the list ("had washed the dishes" and "taken out the trash") each use active voice, describing what Alice did to the dishes and the trash. Changing "the door was locked" from passive to active voice corrects the sentence's error. The corrected sentence reads, "Before Alice left the house, she made sure that she had washed the dishes, taken out the trash, and locked the door."

A sentence should be consistent in its use of verb tense, comparisons, and tone. In the sentence above, "to learn," an infinitive, is being compared to "mastering," a present progressive verb. Things being compared should take on the same grammatical form; that means that "mastering" should be changed to "to master" in order for proper parallel construction to be used. The sentence should read, "It is more difficult to learn to type than it is to master a simple word processing program." "To type" is being compared to "to master"; both are in the infinitive form in this revised case.

This sentence has a problem with parallelism. The items in its list aren't all formatted in the same way: the first two things that we're told Marvin learns to do in his training course are "address customer concerns" and "fill out budget requests," each of these phrases beginning with an infinitive verb. The third thing that Marvin learns to do is "setting up a company account"; in contrast to the previous two infinitive phrases, "setting up a company account" is unnecessarily conjugated to be in the present progressive tense. Since changing the first two items to be in the present progressive tense (as well as the rest of the sentence to make this work grammatically) isn't an option, the answer "and setting up" contains the sentence's error. You could correct the sentence by changing "and setting up" to "and set up," making the corrected sentence, "In his training course, Marvin learned how to address customer concerns, fill out budget requests, and set up a company account."

This sentence has a problem with parallelism. The verbs “communicate” and “solving” should be formatted in the same way, since they are the two things it was "more difficult" for Mary to do. Since only "solving it," and not "communicate," is underlined, "solving it" contains the sentence's error and is the correct answer. The corrected sentence reads, "Although it was easy for Mary to identify the problem, she found it more difficult to communicate with the technical crew and solve it."

The elements in this list do not employ correct parallel structure; there are two nouns and then one adjective. Change the last one to a noun phrase to fix this: "Olympic commentators are experts on the games, dramatic personalities, and enthusiastic fans."