The correct answer is: A. { }
The curly braces ({}) are used to define a REST endpoint. A REST endpoint is a URL that can be used to access a resource. The curly braces are used to group the parameters that are required to access the resource.
For example, the following URL is a REST endpoint:
https://example.com/api/v1/users/{userId}
In this URL, the curly braces are used to group the parameter userId. The value of the userId parameter is used to identify the user that the resource is associated with.
The other options are incorrect. The asterisk (*) is used to represent a wildcard character. The all of the mentioned option is incorrect because the curly braces are the only option that is used to define a REST endpoint. The none of the mentioned option is incorrect because the curly braces are used to define a REST endpoint.