Most commonly "C", because they would want the reader to understand that something is different. Yes, they can change the style whenever they want to, but it would be more meaningful if they did it for a reason.
The sentence that is punctuated correctly is option A. On her Mediterranean cruise, Mamie visited Barcelona, Spain; Nice, France; and Pisa, Italy. A semicolon is used in this sentence because more than one of the units in the series are using the punctuation mark commas.
A because it is the best answer there
Explanation:
it is the opposite what the word means:)