Please check which sentences are correct and what are the differences between them.<br/><br/>I know that the sentence "She left before he came" is correct but please check the following:<br/><br/>1. She had left before he came.<br/><br/>2. She left before he had came.<br/><br/>3. She left before he had written the letter.<br/><br/>4. She left before he had the letter written.<br/><br/>Thanks