Which of the following refers to a failure response resulting in open and unrestricted access or communication?

A. Fail-open

B. Mission-critical

C. Default allow

D. Fail-secure

Answer:A) Fail-open

Explanation:After opening, accessing any operation or function in system or communicating through a network, results in the failure by factor of not being able to be accessed is known as fail-open. The unrestricted access can occur due to several reason like network issue, origin problem etc.

Other options in the given question are incorrect because mission critical, default flow and fail secure are not the situations that occur when after opening, access gets restricted. Thus, the correct option is option (A).