How to get a list of Entities having relationship with Activities (Email, Phone Call, Appointment, etc)

Hello All,

I want to retrieve list of all entities having relationship with Activities. 

I have gone through the below code,

RetrieveAllEntitiesRequest req = new RetrieveAllEntitiesRequest();
req.EntityFilters = EntityFilters.Entity;
req.RetrieveAsIfPublished = true;

RetrieveAllEntitiesResponse response = (RetrieveAllEntitiesResponse) service.Execute(req);
List<string> list = new List<string>();

foreach (var item in response.EntityMetadata)
{
list.Add(item.LogicalName.ToUpper() + " " + item.DisplayName.ToString().ToUpper());
}

list.Sort();