If you want to select multiple levels of Words or Sentences, you have to:
1. Choose the "More" tab;
2. Tap on the "Courses" menu option;
3. Tap on the group you are learning (E.g. Basic Words);
4. Select the levels you want to study.
You can do it both for:
Words
And Sentences
If you have a valid subscription (Premium or with flowers) you will be able to choose any levels.
If you do not have a subscription, you will be able to choose just the first level.
How do I subscribe?
Can I subscribe without money?
How do I change my level?