Which choice displays correct use of commas and proper parallel structure?
a) when i go to the amusement park, i like to ride the roller coaster, eat cotton candy, and hang out, with my friends.
b) when i go to the amusement park, i like to ride the roller coaster, eat cotton candy, and hang out with my friends.
c) when i go to the amusement park i like to ride the roller coaster, eat cotton candy, and hang out with my friends.
d) when i go to the amusement park, i like to ride the roller coaster, eat cotton candy and hanging out with my friends.

The answer is B because each phrase is an infinitive phrase, which is a phrase that starts with "to," which is followed by a verb. For example, in the sentence, "I like to eat ice cream," the phrase "to eat ice cream" is an infinitive phrase since it starts with "to," which is followed by a verb. 

In order for a sentence to be parallel, each of the items separated by commons must be the same type of phrase. In answer choice B, all of the phrases are infinitive phrases. Note, however, that all of the phrases do not start with "to," but that's okay so long as the FIRST phrase does :)

Furthermore, in answer choice B, each phrase is correctly separated by commas, and a comma should be placed after the dependent clause "When I go to the amusement park." 

- That is a lot! But I hope I helped :)