Explanation:

- Public refers to something that is open or accessible to all people, and not restricted in terms of access or audience.

- Option 1: Common - This word is somewhat similar to public, as both refer to things that are widespread or shared by many. It isn't an antonym.

- Option 2: Ready - This implies a state of preparedness and isn't directly related to the concept of public, thus not an antonym.

- Option 3: Private - This is the direct opposite of public. While public spaces or information are available to all, private is restricted to particular individuals or groups.

- Option 4: Restricted - While restricted implies limitations, it does not fully contrast with public as it could refer to limited access within a public context too.

Correct Answer: Option 3: Private