Final answer:
The sentence lacks parallel structure due to the mix of gerunds and an infinitive. For proper parallelism, all elements in the list should share the same grammatical form.
Step-by-step explanation:
The sentence "Ellen likes hiking, the rodeo, and to take afternoon naps" does not have parallel structure. For a sentence to maintain parallelism, similar elements within the sentence should be presented using the same grammatical structure. In this case, the list of activities that Ellen enjoys should follow the same format. We have two gerunds (hiking, the rodeo) and one infinitive (to take).
To correct the sentence for parallelism, it should be rewritten so that each element matches in grammatical form, such as "Ellen likes hiking, attending the rodeo, and taking afternoon naps."