To make a Lightning Web Component (LWC) available in Salesforce Classic, you can embed it in a Visualforce page using Lightning Out.

Option D: Use the Lightning Out JavaScript library to embed the Lightning Web Component in a Visualforce page and add to the page layout.

Lightning Out allows LWCs to be embedded in Visualforce pages.

The Visualforce page can then be included in Salesforce Classic interfaces.

Why Not Other Options:

Option A: Visualforce components cannot directly contain LWCs.

Option B: Wrapping an LWC in an Aura component and surfacing it as a Visualforce tab doesn't make it available on page layouts.

Option C: You cannot invoke an LWC from a Visualforce page using an Apex method call.

Lightning Out for Visualforce:

'Lightning Out is a feature that extends Lightning components to any web page. Use it to embed Lightning web components in a Visualforce page.' --- Lightning Web Components Dev Guide: Use Lightning Web Components in Visualforce Pages

In Aura Components, application events are fired by invoking the fire() method on the event instance.

Option D: fire()

Correct.

To fire an application event, you first get the event instance using cmp.getEvent('eventName') and then call fire() on it.

Example:

var appEvent = $A.get('e.namespace:eventName');

appEvent.setParams({ 'param1' : value1 });

appEvent.fire();

registerEvent is used in the component markup to declare that the component can fire or handle an event.

It is not a method used to fire an event.

There is no fireEvent() method in the Aura framework.

The correct method to fire an event is fire().

Option C: emit()

Incorrect.

emit() is not a method used in Aura components.

This method is commonly used in other frameworks but not in Aura.

Conclusion:

The method used to fire an Aura application event is fire(), which is option D.

Firing Application Events

Incorrect Options:

Option A: registerEvent

Incorrect.

Registering Events

Option B: fireEvent()

Incorrect.

The Lightning Component framework provides:

Option A: Prebuilt components that can be reused

The framework includes a library of base components that developers can use to build custom components and applications.

These components can be reused and combined to create complex UIs.

'The Lightning Component framework provides a set of prebuilt components that you can use to build your own components and applications.' --- Lightning Components Developer Guide

Why Other Options Are Incorrect:

Option B:

The Lightning Component framework is primarily for Lightning Experience and Salesforce mobile app, not for Classic UI.

Option C:

It does not provide extended governor limits; governor limits remain the same.

Option D:

While you can create custom components, the framework does not provide templates in the way described.

To override the Account's standard Edit button in Lightning Experience:

Option A: Lightning component

Implementation:

The Lightning component must implement lightning:actionOverride interface.

<!-- Component code -->

'To override standard actions, create a Lightning component that implements the lightning:actionOverride interface.' --- Lightning Aura Components Developer Guide: Override Standard Actions

Why Other Options Are Incorrect:

Option B: Lightning actions are used for quick actions, not for overriding standard buttons.

Option C: Lightning Flow cannot directly override standard buttons.

Option D: Lightning pages are layouts and cannot override buttons.

To perform DML operations that insert new records and update existing records in a list of Order__c records using the external ID field Order_Number__c, you should use:

Option D: upsert orders Order_Number__c;

Upsert Statement:

The upsert DML operation either inserts or updates records based on whether they already exist.

By specifying the external ID field (Order_Number__c), Salesforce will match existing records based on this field.

Syntax:

upsert orders Order_Number__c;

orders is the list of Order__c records.

Order_Number__c is the external ID field used for matching.

'The upsert statement matches the sObjects with existing records by comparing values of one field. If you don't specify a field, the upsert statement uses the sObject's ID to match data.' --- Apex Developer Guide: Upsert Statements

Why Other Options Are Incorrect:

Option A: merge orders;

The merge statement is used to merge up to three records of the same object type, combining them into one. It is not suitable for upserting multiple records.

Option B: merge orders Order_Number__c;

merge does not accept an external ID field as a parameter.

Option C: upsert orders;

While this will perform an upsert based on the record IDs, it will not use the external ID field Order_Number__c for matching, which may not find existing records without IDs.

Conclusion:

Using upsert orders Order_Number__c; correctly instructs Salesforce to insert or update records based on the external ID field.