How to retrieve the current value of the description field in Dynamics 365 Activity Task record?

    public void Execute(IServiceProvider serviceProvider)
            {
                IPluginExecutionContext context = (IPluginExecutionContext)serviceProvider.GetService((typeof(IPluginExecutionContext)));
                IOrganizationServiceFactory factory = (IOrganizationServiceFactory)serviceProvider.GetService(typeof(IOrganizationServiceFactory));
                IOrganizationService service = factory.CreateOrganizationService(context.UserId);
                ITracingService tracingService = (ITracingService)serviceProvider.GetService(typeof(ITracingService));

                if (context.InputParameters.Contains("Target") && context.InputParameters["Target"] is Entity)
                {
                    Entity task = (Entity)context.InputParameters["Target"];
                    if (task.LogicalName == "task")
                    {
                        ColumnSet cs = new ColumnSet(new string[] { "description", "ownerid" });
                        service.Retrieve("task", task.Id, cs);
                        foreach (KeyValuePair<String, Object> attribute in task.Attributes)
                        {
                            tracingService.Trace(attribute.Key + ": " + attribute.Value);
                        }
                    }
                }
            }