Should be B C regarding this article https://developer.salesforce.com/docs/atlas.en-us.lightning.meta/lightning/events_best_practices.htm

B. Handle low-level events in the event handler and re-fire them as higher-level events.

This practice helps in creating a more organized and maintainable code structure. By re-firing higher-level events, you can ensure that the appropriate components handle the events at different levels of the application hierarchy. This decouples the low-level details from the higher-level business logic, making it easier to manage and understand the code.
C. Reuse the event logic in a component bundle, by putting the logic in the helper.

Placing reusable logic in the helper ensures that your components remain clean and focused on their primary responsibilities. This makes your code more modular and easier to maintain. Reusable logic in the helper can be easily tested and updated without affecting the component’s primary functionality.

C, D are correct.

are these real exam questions .. I wanted to take exam in two days so just wanted to confirm