The correct option for the sentence completion is C. shall have been writing. Let's break down why this is the correct choice and analyze the other options. Explanation of the Correct Answer (C: shall have been writing)

1. Understanding the Context: The sentence states that you started writing at 8:00 a.m. and it is currently 10:00 a.m. By 11:00 a.m., you want to express how long you will have been writing. The time frame here is crucial: you are looking forward to a point in the future (11:00 a.m.) and reflecting on the duration of an action that started in the past (8:00 a.m.).
2. Future Perfect Continuous Tense: The phrase "shall have been writing" is in the future perfect continuous tense. This tense is used to describe an action that will have been ongoing for a certain duration by a specific point in the future. In this case, by 11:00 a.m., you will have been writing for three hours (from 8:00 a.m. to 11:00 a.m.).
3. Structure of the Future Perfect Continuous: The structure of this tense is:
4. Subject + shall/will + have been + present participle (verb+ing).
5. Here, "I" is the subject, "shall" is used (though "will" is also acceptable), "have been" is the auxiliary verb, and "writing" is the present participle.
6. Duration: The phrase "for three hours" indicates the duration of the action, which aligns perfectly with the future perfect continuous tense, as it emphasizes the ongoing nature of the action up to a future point.

Why the Other Options Are Incorrect A. shall be writing - This option uses the future continuous tense, which indicates an action that will be ongoing at a specific time in the future. However, it does not convey the idea of duration or completion by that future time. It would imply that at 11:00 a.m., you will be in the process of writing, but it does not specify how long you have been writing. B. have been writing - This option is in the present perfect continuous tense, which describes an action that started in the past and continues into the present. While it correctly indicates that you have been writing since 8:00 a.m., it does not address the future point of 11:00 a.m. and does not convey the completion aspect that is required in this context. D. am writing - This option is in the present continuous tense, which indicates an action that is currently happening. It does not reflect the future aspect of the sentence and fails to indicate the duration of the writing that will have occurred by 11:00 a.m. Summary of Key Points

• The correct answer is C. shall have been writing because it accurately reflects the future perfect continuous tense, indicating an action that will have been ongoing for a specific duration by a future time.
• The other options do not convey the necessary future aspect or the duration of the action.
• Understanding the different tenses and their implications is crucial for selecting the correct option in such questions.

Revision Summary

• Correct Option: C. shall have been writing (future perfect continuous).
• Context: Action started in the past and will continue until a future point.
• Tense Structure: Subject + shall/will + have been + verb+ing.
• Common Pitfall: Confusing future continuous or present perfect with future perfect continuous.