The correct answer is B. Future perfect
Step-by-step explanation:
In grammar, the future perfect tense is a grammatical tense used to express actions or states that are expected will be completed in the future. This grammatical tense can be identified because it includes the use of "will" that indicates the future along with the use of "have" or "has" depending on the subject and finally the use of the main verb in the past participle. For example, "She will have won the prize by tomorrow".
According to this, the sentence "I will have been here for over four hours by lunchtime" is in future perfect tense because this expresses some action that will be completed in the future "by lunchtime" and includes the future "will have" along with the past participle verb "been" that is common in this tense.