Explanation/Reference:
Explanation:
To create a managed property, add type code to the name, and enable a managed property as a refiner Verify that the user account that performs this procedure is an administrator of the Search service

application.
In Central Administration, in the Application Management section, click Manage service

applications.
On the Manage Service Applications page, click the Search service application in which you want to

create a managed property.
On the Search Administration page, in the Quick Launch, under Queries and Results, click Search

Schema.
On the Managed Properties page, click New Managed Property.

On the New Managed Property page, in the Property name box, in the Name and

description section, type the name of the new managed property, followed by the appropriate type code. For an overview of type codes, see Type codes.
In the Type section, select the appropriate data type.

In the Main characteristics section, set the following selections:

- Queryable
- Refinable: Yes - active or Yes - latent
You can also specify additional settings in this section.
In the Mappings to crawled properties section, click Add a mapping.

In the Crawled property selection dialog box, find the crawled property that you want to map to the

managed property in the list, or search for it by typing the name of the crawled property in the box, and then clicking Find.
Reference: Map a crawled property to a refinable managed property in SharePoint site collection administration Explanation: B, D: The search index consists of a set of files in folders on a server. The content processing component processes crawled items, uses the search schema to map crawled properties to managed properties, and translates the managed properties into a format that is written to the search index. In addition to various full-text indexes, there are separate indexes of the managed properties that are marked as retrievable and those that are marked as queryable.
Note:
* Queryable
Enables querying against thespecific managed property. The managed property name must be included in the query, either specified in the query itself or included in the query programmatically.
* Retrievable
Enables the content of this managed property to be returned in searchresults. Enable this setting for managed properties that are relevant to present in search results.
* Settings on the managed properties determine how content is saved in the search index.
Reference:https://technet.microsoft.com/en-us/library/jj219669.aspx
You need to ensure that properties can be used to refine search results.