Which of the following is an operating system built exclusively to run on a bastion host device?

a. Proprietary OS

b. General OS

c. Reverse proxy

d. Appliance firewall

Answer: a) Proprietary OS

Explanation: Proprietary operating system is the system that is designed for the certain organizations to serve the purpose of designing, development, concepts production etc activities.

Proprietary operating system is constructed and then sold by the companies itself but no alteration can be done by the user in it. E. g.-Mac OS X. Therefore, the correct answer is option (a).