public class Examplefilter {

    Public Static List<Custom_ObjectA> searchforCustom_ObjectA (string Global_Enterprise__c, string Main_HQ__c, String Opportunity__r.Name, String Account_Name__r.Name) {
        Return[SELECT Id, Opportunity__r.Name, Account_Name__r.Name, Main_HQ__c, Global_Enterprise__c
              FROM Custom_ObjectA
              WHERE Main_HQ__c = :Main_HQ__c AND Global_Enterprise__c = :Global_Enterprise__c];
    }
}