Which two methods should a developer implement in a Lightning web component to successfully handle...

To handle the subscription lifecycle of a message channel in a Lightning web component, the developer should implement the subscribe() and unsubscribe() methods from the lightning/messageService module. The subscribe() method returns a subscription object that representsthe connection to the message channel. The developer can use this object to unsubscribe from the message channel later. The unsubscribe() method takes a subscription object as a parameter and removes the listener from the message channel. The developer should call the unsubscribe() method when the component is disconnected from the DOM, such as in the disconnectedCallback() lifecycle hook, to avoid memory leaks and performance issues.

The other options are not correct because:

B. stopListener() is not a valid method for handling the subscription lifecycle of a message channel. There is no such method in the lightning/messageService module or the Lightning web component framework.

C. startListener() is not a valid method for handling the subscription lifecycle of a message channel. There is no such method in the lightning/messageService module or the Lightning web component framework.

References:

Subscribe and Unsubscribe from a Message Channel

Lifecycle Hooks

Use message channel in both direction