Final answer:
Lightning runtime flows offer asynchronous execution, enabling tasks to run in the background for improved web application performance.
Step-by-step explanation:
Lightning runtime flows offer d. Asynchronous execution. The Lightning platform, which is part of the Salesforce ecosystem, allows for the creation of complex, scalable applications that can handle tasks that do not need to be completed immediately. This kind of execution is pivotal for improving the performance of web applications, as it enables tasks to be handled in the background without interrupting the user experience. Furthermore, asynchronous flows contribute to streamlined processes that can occur without the user having to wait for one process to complete before starting another.