Because the part of the sentence before the list is an independent clause, a colon is the correct punctuation mark to use to introduce the list. Because the items in the list are “simple” (in other words, they don’t contain multiple phrases and commas), commas, not semicolons, are the correct punctuation mark to use between each item. Also, since the non-underlined portion of the list already uses commas, the semicolon needs to be changed to a comma to match.

The items in this list should each be separated by a comma. (An "and" could appear between the last two items in the list, but it's not strictly necessary.) The list itself is correctly separated from the second part of the sentence by an em-dash, although a colon would also be acceptable. Therefore, the sentence is correct without any changes.

Because the part of the sentence before the list (“You have”) is not an independent clause (a complete sentence that could stand on its own), a colon should not be used to introduce the list in this sentence. Colons are only used to introduce lists that come after independent clauses.

Here, the list is punctuated correctly. There should be a comma between each item in the list and an additional comma on either side of “Leah,” which modifies “their sister.” (If “their sister, Leah,” was the first or second item in the list, a semicolon would be needed to separate the items for clarity’s sake, but in this version of the sentence it’s not necessary; the relationship of the three people is perfectly clear in this order.)

A comma is needed to separate each item in the list: “preliminary sketches,” “blueprints,” and “plans.”

This sentence is properly punctuated, since a comma is required between each item in a list and the colon is properly used to introduce the list.

The list of features of the event is missing a comma between "bar" and "a" that would correctly distinguish all three features.

A comma should never end a list. The corrected first clause of the sentence would read: "The large fish, the turtles, and the small fish all got along well." A semicolon is appropriate in this sentence to separate the two independent clauses. 

Whenever you have a list of more than two items in a sentence, each item in the list needs to be separated by commas. An apostrophe is correctly used to indicate that the preferences are "Marco's." "In" is the correct preposition in this context. This sentence is correct as it is written.

Whenever you have a list of more than two items in a sentence each item in that list needs to be separated by commas. The best way to correct the sentence above is, "I really hate three chores in particular: cleaning, doing laundry, and mowing the lawn." Note that "doing laundry" and "mowing the lawn" constitute single items in the list. Also note that parallel structure must be maintained within the list.