What does it mean if I only see "Hard" questions when I practice?

If your practice sessions are set to the "Adaptive" difficulty setting, this means they will generate more difficult questions if you've been doing well overall. So, if you see a lot of "Hard" questions, this means you've been doing really well :) If you want to practice a variety of difficulties, just select All Difficulties from the Difficulty drop-down menu on the Practice page!