The Account record includes Invoice roll-up summary fields. This is correct because roll-up summary fields are only available on the master object in a master-detail relationship, and changing the field type to lookup would delete the roll-up summary fields

The two steps that should be suggested to meet these requirements are to select insert null values in settings and to use Data Loader to update leads using the CSV file. Selecting insert null values in settings will allow Data Loader to overwrite existing values with null values. Data Loader is a tool that can import, export, update, or delete large amounts of data.

A cross-object formula field is a formula field that references fields from another object. This can be used to display the value of the Account_Region__c field on Opportunities, as long as there is a relationship between the two objects. Option A, B, and C are not relevant for this requirement.

Given the need to automate a welcome email including a customized survey with customization requirements and a tight timeline, the best approach is:
Use Salesforce Flow to build the survey declaratively to meet the criteria and send it to the customer as an email (B). Flow is a powerful tool for automation in Salesforce, allowing the creation of complex workflows and user interactions without needing to write custom code. It can be used to build a survey and integrate it with email services for automated dispatch.
Working with a developer to create custom Apex and LWC (A) might meet the criteria but would not align with the limited time frame. Managed (C) and unmanaged packages (D) from AppExchange can provide pre-built solutions, but they may not offer the needed customization or could require more setup time than building directly in Flow.
Reference for automating processes with Salesforce Flow:
Salesforce Flow: https://help.salesforce.com/articleView?id=sf.flow_considerations_design.htm&type=5

When a record is submitted for approval, Salesforce automatically locks it, preventing further edits until it is approved, rejected, or recalled.
Why A (Record Lock) is correct:Exact Extract:"When a record is submitted for approval, Salesforce automatically locks the record to prevent users from editing it unless they have 'Modify All Data' permission or are designated as an approver." - Salesforce Help | Approval Processes OverviewThus, the user will receive a message indicating that the record is locked and cannot be edited.
Why A (Record Lock) is correct:Exact Extract:"When a record is submitted for approval, Salesforce automatically locks the record to prevent users from editing it unless they have 'Modify All Data' permission or are designated as an approver." - Salesforce Help | Approval Processes OverviewThus, the user will receive a message indicating that the record is locked and cannot be edited.
Why not B or C:Once locked, no field (including Description) is editable by the submitter.
Why not D:Ownership does not change upon approval submission.
Reference:
Salesforce Help | Approval Processes Overview
Salesforce Platform App Builder Exam Guide | Business Logic and Process Automation