Question

which part of this sentence means every now and then? ayudo a mi hermana de vez en cuando. a mi hermano ayudo a de vez en cuando

Explanation:

The phrase "every now and then" is an adverbial phrase indicating occasional frequency. In Spanish, "de vez en cuando" is a common adverbial phrase with the same meaning. "A mi hermano" means "to my brother" (indicating a recipient), "Ayudo a" means "I help" (verb + preposition), neither of which relate to the frequency meaning.

Answer:

De vez en cuando