As early stated at the beginning of the course, all lessons, homeworks and quizes should have to be taken until 11th of februar. After this date all link become disabled and I think this is your case. Probably you will have to enroll again for the next MOOC on PL/SQL fundamentals.
You are Correct.
If you are interested, you can enroll yourself into any future runs of this MOOC and try the quizzes again.
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