Final answer:
The correct answer is 'will be sleeping'.
Step-by-step explanation:
The correct answer to fill in the blank is will be sleeping. The verb phrase 'will be sleeping' indicates a future action, showing that the speaker plans to sleep when the plane lands. It is in the future progressive tense, expressing an ongoing action at a specific time in the future. For example, 'We will be sleeping when the plane lands, so we will be well-rested when we arrive at our destination.'
Learn more about Verb tenses in English