Global applications can use Automated Test Framework and Flow Designer features, but not Source Control and Delegated Development features. Source Control and Delegated Development features are only available to scoped applications . Reference: [Global vs Scoped Applications], [Delegated Development]

The correct combination of statements is a, b, and d. These are possible reasons to build custom applications on ServiceNow:
To replace outdated, inadequate, custom business applications and processes. Building custom applications on ServiceNow can help digitize and automate manual or legacy processes that are not covered by existing ServiceNow solutions. This can improve efficiency, data quality, user experience, and innovation.
To extend service delivery and management to all enterprise departments. Building custom applications on ServiceNow can help provide consistent and scalable services across different functions and teams in the organization. This can enhance collaboration, visibility, productivity, and customer satisfaction.
To extend the value of ServiceNow. Building custom applications on ServiceNow can help leverage the capabilities and benefits of the Now Platform, such as low-code development tools, workflow automation engine, AI-powered insights, security operations, etc. This can increase agility, resilience, performance, and value.
The statement c is not a valid reason to build custom applications on ServiceNow:
To allow users full access to all ServiceNow tables, records, and fields. Building custom applications on ServiceNow does not imply granting users full access to all data and objects in ServiceNow. Access control rules still apply to custom applications and their components to ensure security and compliance. Reference: Build Custom Apps in ServiceNow - eBook

https://docs.servicenow.com/bundle/rome-platform-administration/page/administer/reference-pages/task/schedule-report.html Generate and distribute scheduled reports via email.
A report is a graphical representation of data from one or more tables in ServiceNow. The following are true for reports in ServiceNow:
Can be a graphical representation of data. This is true because reports can use various chart types, such as pie, bar, line, or gauge, to visualize data in a meaningful way.
Can be run on demand by authorized users. This is true because reports can be accessed from the Reports menu or the Report Navigator and run by users who have the appropriate roles and permissions to view the data.
Can be scheduled to be run and distributed by email. This is true because reports can be configured to run at a specific time and frequency and send the results to one or more email recipients.
The following are not true for reports in ServiceNow:
Any user can see any report shared with them. This is false because users can only see reports that are shared with them if they also have access to the data source of the report. For example, a user who does not have the itil role cannot see a report based on the incident table, even if the report is shared with them.
All users can generate reports on any table. This is false because users can only generate reports on tables that they have access to and that are enabled for reporting. For example, a user who does not have the admin role cannot generate reports on the sys_user table, which is the table for user records. Reference: Reports, Report Security

Tables that extend a table inherit the parent's fields. Extending a table means creating a child table that shares the same columns and business logic as the parent table. For example, the Incident table extends the Task table, which means that all fields defined on the Task table are also available on the Incident table. Extending a table allows for reusing existing fields and behaviors without duplicating them on multiple tables. Reference: Table extension and classes

A possible reason to build a custom app is to fulfill a specific use case on internal processes. For example, you may want to digitize a manual process that is not covered by an existing ServiceNow solution, such as managing inventory, tracking expenses, or scheduling events. Building a custom app on the Now Platform can help you automate workflows, improve data quality, and provide better user experiences. The other options are not valid reasons to build a custom app. To avoid using a code repository like GitHub or GitLab is not a reason to build a custom app, as you can still use source control integration with your custom app development. To create a custom integration for a 3rd party system is not a reason to build a custom app, as you can use integration tools such as IntegrationHub or REST APIs to connect with external systems without creating an app. To replace ServiceNow base tables is not a reason to build a custom app, as it is not recommended to modify or delete base tables that are essential for ServiceNow functionality. Reference: Build Custom Apps in ServiceNow - eBook