Choose the correct form of the verb. His parents ... (run) now.

The correct answer is 'aren't running'. Explanation: The sentence requires the present continuous tense because of the word 'now', which indicates an action happening at the present moment. 'His parents' is plural, so we need a plural form of the auxiliary verb 'to be' (are). Therefore, the correct form is 'are not running' or 'aren't running'.