A business requires a legacy version of an application to operate but the application cannot...

Mitigate is the risk treatment option that has been applied by implementing a firewall in front of the legacy application because it helps to reduce the impact or probability of a risk. Mitigate is a process of taking actions to lessen the negative effects of a risk, such as implementing security controls, policies, or procedures. A firewall is a security device that monitors and filters the network traffic between the legacy application and the external network, blocking or allowing packets based on predefined rules. A firewall helps to mitigate the risk of unauthorized access, exploitation, or attack on the legacy application that cannot be patched. Therefore, mitigate is the correct answer.