By this time tomorrow, Annie . . . . . . . . through space for nineteen hours.

Solution (By Examveda Team)

The correct answer is B: will have been flying.
Let's break down why:
This question tests your understanding of future perfect continuous tense.
The future perfect continuous tense describes an action that will have been in progress for a period of time at a specific point in the future.
The phrase "By this time tomorrow" indicates a specific point in the future.
The phrase "for nineteen hours" indicates a duration of time.
Therefore, we need a tense that shows an action continuing up to a point in the future.
Option A: will be flying is the future continuous tense. It describes an action in progress at a specific time in the future, but doesn't emphasize the duration.
Option B: will have been flying is the future perfect continuous tense. It correctly shows that Annie's flying will have been ongoing for 19 hours by the time tomorrow comes.
Option C: flies is the simple present tense. It is incorrect because it doesn't refer to the future.
Option D: will fly is the simple future tense. It describes a single action in the future, not a continuous action.
Option E: is going to fly is the future tense (be going to). It is close, but it does not show the duration of the flight as accurately as the future perfect continuous.
Therefore, only "will have been flying" correctly conveys that the action of flying will have been in progress for a continuous duration of 19 hours by a specific time in the future ("by this time tomorrow").