The answer is the first option: <em><u>"On my summer trip, I plan to visit Chicago and Los Angeles."</u></em>
The Associated Press Style guide states some rules for documents to have a common understanding. Some of the rules state that we must spell out numbers from one to nine and for the rest, they should use figures (Which is what happens in the second option). Another rule lists some cities that don't need the state name such as Pennsylvania, Boston San Francisco, and Los Angeles. (Which is what happens in the third and fourth options). And as we can see in the last option, the commas rule after "and/or" is missing.
The AP style guide also states rules about quotation, punctuation, numbers, names, cities, dates, days, capitalizations, and others.
