This sentence has misplaced the colon. The colon should come after the word "include" since that word marks the end of the first clause. Note that colons combine two clauses when the second one explains or describes something about the first clause. The correct choice is, "market caps on the stock market include: Roundree, Gargle, and Mousecow."

This sentence uses a colon where one is not necessary. Colons are used to join two clauses when the second clause describes something about the first clause. In this sentence, however, there is only one clause (the word "that" does not begin a new clause, but an indirect statement phrase). The correct choice is, "that he was going in the wrong direction."

This sentence contains an error in the placement of the colon. Colons are used to join two clauses when the second clause explains something about the first clause. In this sentence, however, there is only one clause (colons never split clauses). It is best to omit the colon. The correct choice is, "newest creation was incredibly delicious."

This sentence contains a colon where a semicolon is necessary. Colons join two related clauses when the second one explains something about the preceding clause. In this sentence, however, the phrase "so far, he had shaved one minute off of his time per mile" does not explain why the subject tries to improve his timing or how he goes about doing that; it simply tells us his progress in this endeavor. Semicolons join two related independent clauses without the use of a conjunction. This is the appropriate choice. The correct answer is, "improve his running time; so far, he had shaved."

This sentence contains a colon where a comma is necessary. The phrase "In the past" is an example of an introductory phrase, explaining information necessary to the context of the sentence, but outside of the main sentence, grammatically. These types of phrases must be followed by a comma in order to separate them from the rest of the sentence. The correct answer choice is, "In the past, many civilizations have looked."

This sentence uses a colon where one is not necessary. Colons are used to join clauses when the second clause explains something about the first one. In this sentence, however, the colon appears in the midst of the clause, before a preposition. Colons should never be used in this way (never in conjunction with a preposition). The correct choice is, "the weekdays when less people were in the stores."

Colons can be used to set off a list. In this case the list is composed of three clauses. The sentence is correct as is. All of the other answer choices contain punctuation errors.

A colon can be correctly used to set up a definition. In this case, we are defining the definition which the subjects of the sentence pulled from the dictionary. Using an em dash is inappropriate. Em dashes are typically used to set up an interrupting clause that is not entirely relevant to the sentence. Using a semi-colon would also be inappropriate. The best answer choice simply uses a colon, rather than commas which result in punctuation errors. "Then" and "than" are commonly confused but "then," in this case, would be incorrect.

This sentence contains a semicolon where a colon should be. Note that semicolons only join independent clauses. The words "mats, oil, tools, and more" is  not an independent clause. Furthermore, these words describe a part of the preceding clause: what the subject bought. Colons combine two clauses when the second clause explains something about the first one. Additionally, the words "mats, oil, tools, and more" are in a list, so each item in the list should be separated by commas. The correct choice is, "his car: mats, oil, tools, and more."

This sentence contains a colon where one is not necessary. Colons are used to combine two related clauses when the second clause explains something about the first one. The colon used here, however, appears in the middle of a clause, which never happens with colons. The colon should be omitted and no additional punctuation is necessary. The answer is, "They liked to sing the songs."