My personal opinion is that it could be nice feature in FCC to have some kind of checkpoints for every lecture where i must to pass some test without any hints. If i can’t pass that test i can easy return back to the current lecture start point and repeat every question.
For me it is better to check my memory by small steps.
But there is no such option. You just do the tasks and go forward. All previous tasks become forgotten after 30 minutes.