Why doesit ask the same phrase 10 x
My guess is that repetition is the key to learning something (or maybe it takes time to make a new phrase, as they have to match it up with a lot of possible translations, and they have only made enough to get DuoLingo started so far).
Because otherwise you wouldn't remember.
I think part of it is the limited vocabulary in the first levels. Once you get to the more advanced levels there is still repetition, but its not as bad.