Answer: D) Boating, waterskiing, and sunbathing are three activities in which a person can take part at the lake.
Step-by-step explanation: Parallelism or parallel structure is a literary device that consists in the repetition of the grammatical structure of words or phrases in a text. In the given sentences we can see a list of elements, in order to them to be correct, they must be consistent in the form of the nouns and verbs (they should be all in the infinitive form or all in the gerund form), so the options B and D use parallel structure correctly, but option B have a comma before the verb which is incorrect (we should not use commas to separate the subject from the verb), so the correct answer is option D.