This sentence is a run-on sentence because it contains two independent clauses, "The quetzal is a tropical bird that is famous for its vivid plumage" and "it is also important in Mayan mythology." To correctly connect these two sentences, you can use a semicolon or a comma followed by a conjunction. (Writing the independent clauses as two separate sentences would also be a way to correct the error.) The only answer choice that correctly uses one of these methods is "The quetzal is a tropical bird that is famous for its vivid plumage; it is also important in Mayan mythology."

A sentence with two independent clauses must have both clauses be able to stand as complete sentences, and be connected to each other in meaning through a conjunction. "And many students studied with him," is the only choice that fits those parameters.

The answer choice "written by poet Langston Hughes, and even today, it is widely regarded as one of the most influential works" is correct because it results in a sentence in which two independent clauses are separated by a conjunction followed by a comma.

The original text and answer choice "written by poet Langston Hughes; and even today, it is widely regarded to be one of the most influential works" uses a semicolon incorrectly. Sentences can be combined with a comma followed by a conjunction or with a semicolon, but not with a semicolon followed by a conjunction.

The answer choices "written by poet Langston Hughes, even today, it is widely regarded as one of the most influential works" and "written by poet Langston Hughes, it is widely regarded, even today, as one of the most influential works" create run-on sentences and are therefore incorrect.

The underlined portion of the sentence stands oddly next to the preceding phrase, as it is in no way connected to the preceding phrase. The phrase needs to be changed so that it appropriately links with the first part of the sentence. "With vendors finding their profits increasing with each event" is the correct answer choice.

This is an example of a sentence fragment. There is no subject for this clause. The correct choice is "She worked on the project throughout the night" because it adds a subject and alters the verb in the appropriate way so that it agrees with the pronoun.

This is an example of a sentence fragment. It is lacking a subject. The most clear and concise choice that fixes this error is, "Kara loves fishing in the pond." The other choices are wordy or redundant.

This sentence is not a sentence: it is a segment fragment. The correct choice is, "Gina, who is the authority in her field, just published a new book" because it completes the sentence. The other choices are also fragments or just do not make any sense.

The example above is a sentence fragment; the word "studying" by itself is not a verb in English and every sentence must have a subject and a verb at least. The correct choice is, "Tiffany was studying for her exams." This is the only choice that fixes this error.

The above example is a sentence fragment. Even though the sentence contains a subject and verb, the verb "to be able" must have an object - it makes no sense by itself or without context. The choice that fixes this error is, "Trina was not able to finish her assignment." Note that a colon would be inappropriate after "able" because colons are used to join two separate clauses when the second one explains something about the first. This sentence only contains one clause.

The example above is not a sentence but a sentence fragment. Every proper sentence must have a subject and a main verb; this sentence contains neither (note that infinitives, while a verb form, do not function as a main verb). The correct choice is "They were unable to fix the device."