スーパーに行ったら、牛乳をかってきてくれる？
The Bunpro Translation of the above is:
If you go to the supermarket, could you buy some milk (and come back)? [for me]
If you go to the supermarket, could you buy some milk (and come back)? [for me]
Since we're asking for a favor (it sounds like we are), then why isn't kureru in the Te form?
