Convert the sentence from Active to Passive voice: "I will write an essay." Choose the correct passive form.

Introduction / Context:
Voice change questions test your command of English grammar, especially your ability to move between active and passive constructions without changing the essential meaning, tense, or aspect of the sentence. Here, you are asked to convert "I will write an essay" from active voice to passive voice. The subject, object, and auxiliary verb must all be adjusted correctly while preserving the original future tense.

Given Data / Assumptions:
- Active sentence: "I will write an essay."
- Subject in active voice: "I".
- Object in active voice: "an essay".
- Tense and aspect: simple future ("will write").
- Requirement: Express the same idea in passive voice without changing the time reference or meaning.

Concept / Approach:
To form the passive, the object of the active sentence becomes the subject of the passive sentence, and the original subject may appear at the end, introduced by "by". For simple future tense, the passive structure is: "will be" + past participle of the main verb. Therefore, "will write" becomes "will be written", and "an essay" moves to the front as the new subject. The agent "I" appears at the end as "by me" if we choose to mention it.

Step-by-Step Solution:
Step 1: Identify the verb phrase and tense in the active sentence: "will write" is simple future. Step 2: Move the object "an essay" to the subject position in the passive sentence. Step 3: Form the passive auxiliary: "will be" plus "written", the past participle of "write". Step 4: Place the original subject "I" after the verb phrase, using the preposition "by". Step 5: Combine to get "An essay will be written by me."

Verification / Alternative check:
Check each option for tense consistency. The original sentence is in simple future, so the passive must also be simple future. "An essay will have been written by me" (option A) is future perfect, which changes the time reference. "An essay has been written by me" (option C) is present perfect, and "An essay had been written by me" (option D) is past perfect. Only "An essay will be written by me" keeps the same time meaning as the original sentence.

Why Other Options Are Wrong:
- Option A: Uses "will have been written", which expresses completion before a future point, not the simple plan or intention expressed in the original sentence.
- Option C: Indicates an action completed in the recent past, not a future action.
- Option D: Refers to an action completed before another past event and is not equivalent to the future tense of the original.

Common Pitfalls:
Candidates often ignore the tense in the original sentence and pick any grammatically correct passive form. Always match the tense and aspect first. Also, do not change the meaning by adding or removing time references. Remember the general formula: simple future active "will + base verb" becomes passive "will be + past participle".

Final Answer:
The correct passive voice form is An essay will be written by me.