The correct answer is C. A letter is written by Rajat.
A. A letter wrote by Rajat is grammatically incorrect. The verb “write” takes an object, so the correct form would be “Rajat wrote a letter.”
B. A letter was to be written by Rajat is in the passive voice. The passive voice is used when the focus is on the action rather than the agent performing the action. In this case, the focus is on the fact that a letter was written, not on who wrote it.
D. A letter is to be written by Rajat is also in the passive voice. However, in this case, the passive voice is used to express a future action. The sentence means that Rajat will write a letter in the future.
In conclusion, the correct answer is C. A letter is written by Rajat.