Modern web service systems are designed for high availability and resiliency. Which concept pertains to the ability to detect problems within a system, environment, or application and programmatically invoke redundant systems or processes for mitigation? 

Answer options:

A. Elasticity
B. Redundancy
C. Fault tolerance
D. Automation

C

Fault tolerance allows a system to continue functioning, even with degraded performance, if portions of it fail or degrade, without the entire system or service being taken down. It can detect problems within a service and invoke compensating systems or functions to keep functionality going. Although redundancy is similar to fault tolerance, it is more focused on having additional copies of systems available, either active or passive, that can take up services if one system goes down. Elasticity pertains to the ability of a system to resize to meet demands, but it is not focused on system failures. Automation, and its role in maintaining large systems with minimal intervention, is not directly related to fault tolerance.