Answer:
The answer is D. Implement STP or RSTP.
Explanation:
STP (Spanning Tree Protocol) was built to serve as a remedy for network issues. Existing before switches were developed, it works as a substitute for a switch when a switch is wired incorrectly (as seen in the question) or when it fails. STP has two roles:
RSTP (Rapid Spanning Tree Protocol) was built to optimize the standard STP. When there is a topology change, spanning tree convergence is much faster than the standard STP.
To prevent network failure in the future, STP or RSTP should be implemented.