汉译英：你写信时我正在看书

I was reading while you were writing a letter .
希望能对您有所帮助吧 呵呵

i was reading a book while you were writing a letter

I was reading while you were writing letters.

I am reading a book while you are writing a letter.

While you were writing letters, I was reading a book

I was reading while you was writting letters

I was reading a book when you wrote the letter.

While you are writing a letter, I am reading( a book).
希望对你有所帮助，祝你快乐每一天！(*^__^*)