Singular :

The correct answer is: B. Ancient

An ancient thing is one that existed in the distant past. It is often used to describe something that is very old and has been around for a long time. For example, the pyramids of Egypt are ancient structures that were built over 4,500 years ago.

The other options are not singular.

• Dull is an adjective that means not interesting or exciting.
• Common is an adjective that means found or happening often.
• Social is an adjective that means relating to or involving society or social relationships.