A developer is building a custom component in Lightning web components (LWC) that has a...

 The correct way to demonstrate the passing of a message from the grandchild component to the grandparentcomponent in LWC is to use the PubSub library. The PubSub library is a utility that enables Lightning web components to communicate across the DOM tree without using intermediaries. The grandchild component can publish a message to a channel, and the grandparent component can subscribe to that channel and receive the message. This way, the communication is decoupled and does not depend on the component hierarchy. Option B shows the correct syntax for using the PubSub library to pass a message from the grandchild component to the grandparent component. Option A is incorrect because it uses the @api decorator to expose a property on the grandchild component, which is not a valid way to communicate with the grandparent component. Option C is incorrect becauseit uses the @wire decorator to wire a property on the grandchild component to a function on the grandparent component, which is also not a valid way to communicate with the grandparent component. Option D is incorrect because it uses the @track decorator to track a property on the grandchild component, which is not a valid way to communicate with the grandparent component. References: Communicate Across the DOM |Lightning Web Components Developer Guide, Child to grandparent communication in LWC, PubSub Library for Lightning Web Components