Retrive all Activities for specific Case in MS-CRM 4.0 through QueryExpression, FilterExpression and ConditionExpression

Database Query: "SELECT * FROM ActivityPointerBase WHERE RegardingObjectId = 'BF0F0BD9-FCCA-E011-9E6F-00155DE0140E'"

static void GetActivitiesFromSpecificEntity()

        {

            CRMHelper objCRMHelper = new CRMHelper();

            CrmService service = objCRMHelper.GetCRMService();

            AllColumns activityPointerBaseColumns = new AllColumns();

            QueryExpression query = new QueryExpression();

            query.ColumnSet = activityPointerBaseColumns;

            query.EntityName = EntityName.activitypointer.ToString();

            //WHERE CONDITION

            FilterExpression activityFilter = new FilterExpression();

            ConditionExpression activityCondition = new ConditionExpression();

            activityCondition.AttributeName = "regardingobjectid";

            activityCondition.Operator = ConditionOperator.Equal;

            activityCondition.Values = new object[] { "BF0F0BD9-FCCA-E011-9E6F-00155DE0140E" };//Case ID

            activityFilter.Conditions = new ConditionExpression[] { activityCondition };

            query.Criteria = activityFilter;

            BusinessEntityCollection result = service.RetrieveMultiple(query);

            if (result.BusinessEntities.Length > 0)

            {

                foreach (BusinessEntity objBE in result.BusinessEntities)

                {

                }

            }

        }