I think the correct answer among the choices listed above is option C. The future progressive tense is the verb form that should be used to indicate the progressive tense. This indicates an action is something that will be happening in the future.
Option C. The verb form that is used to indicate the progressive tense is the future progressive.
Explanation:
The progressive form is a verb tense used to show an ongoing action in progress at some point in time. Verbs can appear in any of the three progressive tenses: present progressive, past progressive and future progressive.
In the case of the future progressive, the tense structure is form by using the modal "will" + "be" + the present participle of the verb, with an in- ending.
I believe answer "c" contains the error. Instead of the verb "is," it should be the verb "are" because if you were to replace "Both Clara and Nathan" with the plural pronoun "they," the verb "are" would make the most sense.