https://docs.servicenow.com/bundle/rome-application-development/page/build/applications/concept/c_DefaultDesignAccessPermissions.html The baseline behavior of a table in a privately-scoped application is that all application scopes can read from the table. A privately-scoped application is an application that restricts write access to its tables and resources to scripts within the same scope. However, read access is allowed by default for all scopes, unless the administrator explicitly denies it using an Access Control rule. This allows for data sharing between different applications while maintaining data integrity and security. Reference: [Product Documentation | ServiceNow], [Advantages of Scoped Applications in ServiceNow]

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To replace outdated, inadequate, custom business applications and processes.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/tokyo-servicenow-platform/page/administer/notification/task/t_CreateANotification.html Reference:
An Email Notification is a record that defines the content and conditions for sending an email message from the ServiceNow platform. The following are configured in an Email Notification:
Who will receive the notification. This is specified by the Recipients related list, which can include users, groups, email addresses, or scripts that return email addresses.
What content will be in the notification. This is specified by the Subject and Message HTML fields, which can include variables, scripts, or templates to dynamically generate the email content.
When to send the notification. This is specified by the When to send tab, which defines the conditions and events that trigger the email notification.
The following is not configured in an Email Notification:
How to send the notification. This is not a configuration option for an Email Notification. The platform uses the SMTP protocol to send email messages, and the email properties control the email server settings and behavior. Reference: Email Notifications, Get Started with Notifications