Which sentence demonstrates proper parallel structure?

• A. I like swimming, biking, and running.
• B. I like swimming, biking ran.
• C. I like swimming and biking, and running.
• D. I like swimming, biking and running.

Answer: (D)

Parallel structure means listing items in the same grammatical form so the sentence has a balanced, smooth rhythm. In this sentence, the things you like are swimming, biking, and running—each item is a gerund (the -ing form) acting as a noun. That keeps the list uniform after the verb like, which is exactly what parallel structure calls for.

The other options break that pattern in a couple of ways. One option uses a past-tense verb (ran) instead of an -ing form, so the items don’t share the same shape. Another option tries to treat two items as a unit (“swimming and biking”) and then adds a third item (“running”), which disturbs the even, three-item list. This sentence keeps all items in the same form and links them with the same kind of punctuation, producing a clean, parallel list.