To convert a present simple sentence into past simple, we change the verb to its past tense.
- "He wrote a letter" is the correct past simple form of "He writes a letter."
- "He has written a letter" is present perfect tense, which is incorrect here.
- "He write a letter" uses the present tense and is incorrect.
- "He send a written letter" is not grammatically correct. To convert a present simple sentence to past simple, change the verb to its past form. For "write," the past form is "wrote."