In the original sentence, "Sunita is writing a letter," the subject is "Sunita," the verb is "is writing," and the object is "a letter."

In the passive voice, the structure changes, and the object of the active sentence becomes the subject of the passive sentence. Additionally, the verb is changed to a passive form, and the original subject may or may not be included as the agent.

Here's the breakdown of the transformation:

Original sentence:

• Subject: Sunita
• Verb: is writing
• Object: a letter

Passive voice sentence:

• Subject: A letter (the object of the original sentence)
• Verb: is being written (passive form of "is writing")
• Agent: by Sunita (optional; you can include or omit the agent)

So, "A letter is being written by Sunita" is a grammatically correct passive voice transformation of the given sentence.