Discovery can provide information about the relationships between configuration items (CIs), including applications and hosts. Application relationships are the connections between applications that run on different hosts or servers, such as web servers, databases, load balancers, etc. Host relationships are the connections between applications and the hosts or servers that they run on, such as Windows, Linux, Unix, etc. Discovery can identify these relationships using various methods, such as probes, sensors, patterns, file- based discovery, etc. Discovery can also create and update these relationships in the CMDB, using the Depends on::Used by or Runs on::Runs relationship types.
1: Discovery Relationship Creation, Application Discovery Mapping Overview, IT Discovery - Application Dependency Mapping

In ServiceNow Discovery, relationships between Configuration Items (CIs) in a horizontal pattern are created using the "Create Relation/Reference" operation. This operation allows the pattern to define and establish relationships or references between discovered CIs, based on the information gathered during the discovery process. Options B and C are incorrect as relationships are not automatically created nor is it true that they cannot be created via patterns. Option D, "Create Connections," is not a standard operation in this context.
References= ServiceNow Discovery documentation, specifically the sections on creating and managing horizontal discovery patterns.

To launch any pattern, you need to specify the CI classification and the CI type. The CI classification determines the table where the discovered CI is stored in the CMDB, and the CI type defines the specific attributes and relationships of the CI. For example, if you want to discover a Windows server, you need to select the CI classification as cmdb_ci_win_server and the CI type as Windows Server. These choices are mandatory for any pattern, as they enable Discovery to identify and classify the CIs correctly.
1: Patterns and horizontal discovery, Available discovery patterns
Reference: https://docs.servicenow.com/bundle/quebec-it-operations-management/page/product/discovery/concept/c-UsingPatternsForHorizontalDiscovery.html

Agent Collector is the component that executes the osquery commands on agents to gather attribute details from a CI. Agent Collector is a feature of the Agent Client Collector (ACC) for Discovery, which is an integration that enables ServiceNow Discovery to use osquery to collect data from Linux and Windows devices that have the Elastic Agent installed1. Agent Collector allows you to define osquery queries and assign them to policies that target specific devices or groups of devices2. Agent Collector then runs the queries on the agents and sends the results back to the instance, where they are processed by the Agent Listener and stored in the CMDB3.
1: Agent Client Collector for Discovery - ServiceNow 2: Create an Agent Collector policy - ServiceNow 3: Agent Client Collector for Discovery architecture - ServiceNow