or you must learn step by step...but in the optiosn is not study at all...I feel cheated :)
I guess "one step at a time" should be accepted too.
that's rather "ein Schritt nach dem anderen".
What is the difference between you must and you have to? There must be one because Duolingo accepts one but not the other.
Not enough people have reported the other. That, or so many people are reporting problems, that they don't have time to get to it.
You must learn step for step.
The correct English expression is "step by step."
"you have to walk to learn how to walk" seems closer to the original
By no means that would be correct...