Hello I am wondering whether the preposition "to" at the end of the following sentences can also be left out: 1. Did you post my letter? - Oh, sorry, I forgot (to). 2. I can't go out with you this evening. Sorry. - Oh, but you promised (to). 3. Why did you email your mother again? - Because she asked me (to). 4. Do you think you'll apply for that job? - Yes, I've definitely decided (to). If to can be left out, is there any difference in style?