Application developers can specify which ServiceNow page a user sees after submitting a new record using the Record Producer UI by writing a script in the Record Producer's Script field: producer.redirect = "<URL>";. This script sets the redirect property of the producer object to the URL of the desired page. For example, producer.redirect = "home.do"; will redirect the user to the homepage after submitting the record. The other options are not valid ways to specify the redirect page for a Record Producer. Reference: Populate record producer data and redirect users

The ServiceNow platform is designed to create applications that use forms, workflow, and reporting to solve business problems. Forms are used to interact with data stored in tables, workflow is used to automate and orchestrate processes, and reporting is used to visualize and analyze dat a. The platform does not require low-level programming libraries or multimedia features, as it provides standard tools and technologies for application development.
Reference = ServiceNow Certified Application Developer Exam Specification, Application Development Platform - 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To replace outdated, inadequate, custom business applications and processes.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