Which sentence demonstrates faulty parallelism?

• A. She likes swimming, biking, and to run.
• B. She likes swimming, biking, and running.
• C. She liked swimming and biking.
• D. She will swim, bike, and run.

Answer: (A)

Parallel structure means keeping the same grammatical form when you list items. When you have a verb like likes, the items that follow should all be the same part of speech.

In this sentence, the list after likes mixes forms. swimming and biking are gerunds ( nouns formed from verbs with -ing ), but to run is an infinitive. That mismatch makes the sequence feel unbalanced and disrupts the rhythm of the sentence.

A smooth fix would keep all items the same form, for example: swimming, biking, and running (all gerunds), or to swim, to bike, and to run (all infinitives). The other sentences shown maintain a consistent form: liked swimming and biking uses two gerunds; will swim, bike, and run uses base verb forms after will, all parallel.

So the sentence with the mixed form demonstrates faulty parallelism, which is why it’s the best choice for illustrating the issue.