I normally roll my eyes when I see folks promoting their links for the Coinbase quizzes, primarily because I assume that most of us have already done them. This one is new, though, and provides $4 worth of OXT per lesson/quiz, which you can then convert to BTC/Alt-coins.

Ref-link: https://coinbase.com/earn/oxt/invite/8xbrnf35

Using that allows you to skip their 'wait-list' and start the lessons immediately. Took me about 7 minutes to finish. FULL DISCLOSURE: Following my ref link grants me $10 in OXT. So thank you in advance if you decide to do them!