A mobile app team is discussing how to use Firebase Analytics to gain insights into their app's performance. For each of the following objectives, identify which feature of Firebase Analytics should be primarily used:
- Objective I: Understanding which features of the app are most engaging to users based on how long and how frequently they use the app.
- Objective II: Determining which in-app activities are leading to purchases or other key conversions.
- Objective III: Developing targeted marketing strategies for different demographic groups using the app.
- Objective IV: Identifying which marketing channels are bringing the most users to the app.
Match each objective with the appropriate Firebase Analytics feature.