Company A acquired Company B. During an audit, a security engineer found Company B's environment was inadequately patched. In response, Company A placed a firewall between the two environments until…

Accepting risk involves acknowledging it without taking action to reduce it, which contradicts the active measure of placing a firewall.

Avoiding risk means eliminating the activity causing the risk, which would imply not acquiring Company B or immediately decommissioning its systems.

Transferring risk involves shifting the financial burden or responsibility to another party, such as through insurance, which is not what was done by implementing a firewall.

Mitigate is the risk-handling technique used when an organization implements controls or countermeasures to reduce the likelihood or impact of a risk. Placing a firewall between the two environments directly reduces the risk of Company B's inadequately patched systems affecting Company A's network by controlling access, thereby mitigating the risk.