The correct answer is B. Fault Management API. The Fault Management API can be used to identify the root cause(s) of issues in the network, such as hardware or software faults, configuration errors, and other problems. It provides a unified interface to receive and analyze fault information from multiple network elements.

The API that can identify the root cause(s) of issues in the network is the Fault Management API. This API allows network operators to monitor network faults and events in real-time, and diagnose and resolve issues quickly and efficiently. It provides information about the root cause(s) of the fault and the affected network elements, as well as enabling automated fault handling and resolution.