I am sorry there is a full stopWhen you ask "which one is right", there is an implication that the other one is wrong, but that is not the case. Both are right (*). Often one is better because it's more natural, and that's usually the on with "going to", but in this example there is not enough context to support that choice.
(*) Strictly speaking, both are wrong because the comma is the wrong connector to use here. You could use a semicolon or a dash, but it's probably best simply to make it two separate sentences (i.e. use a full stop): ..be skilled. They...
Also note that, as with full stops, we do not put a space before a comma:
Wrong , wrong .
You have edited #1 to change the commas to full stops, but there is still (incorrectly) a space before them, and you need to change they to They.
I have a slight preference for the "will" version here, but would not consider the "are going to" one wrong.
Did the test question actually ask "Which one is right" or "Which one is better"?