Populate Regarding Field In CRM 2013 Using Plugin

Populate regarding work with creating records.

Here are my code (Im Creating new task with populated Regarding Field):

 Entity newTask = new Entity("task");
 newTask["subject"] = "Document" + DateTime.Now.ToShortDateString();
 newTask["description"] = "Description";
 newTask["regardingobjectid"] = new Microsoft.Xrm.Sdk.EntityReference("account", account.Id);
 service.Create(newTask);

Result:

New Task will be created with subject field, description field and regarding field with value.