The correct option is C Simple Future Tense
The tense of a sentence denotes a time, whether it is the time now (present), time then (past) or the time to come (future). The verb of a sentence has most to do with the tense. The form in the given sentence 'will speak' is in the simple future tense, it describes an action that is yet to take place. The form of the simple future tense is will + verb, hence option C is correct. The future progressive tense, commonly called the future continuous tense, is of the form will be + present participle (verb form that ends in -ing). It's not the same as the given sentence hence option A is incorrect. The future perfect tense is of the form shall/will have + past participle. The future perfect continuous tense is of the form 'will have been + present participle', the given sentence does not have any of these forms, hence options B and D are incorrect.