For a language learning app, identify which two features from the list below are potential core product-side levers that can effectively improve retention rates:
- Lever I: Customizable learning paths that adapt to user performance and feedback.
- Lever II: Community forums where users can engage in language practice with peers.
- Lever III: Regular push notifications reminding users to complete daily lessons.
- Lever IV: Periodic discounts on subscription renewals for long-term users.