Add picklist custom field to Entity in Dynamics CRM

In the Dyna开发者_开发技巧mics CRM environment, I have created the custom entity as Countries. there is another by default entity under the Sales is: Opportunity. I create the N to N relationship between both (Opportunity and countries).

Then when I go to opportunity editing page that is opportunity entity under the edit mode.I added the new field name as Select Country (following map : Settings-> Customizations-> Opportunity -> Forms and Views -> Form-> double click->Add Field). Got the field list. I found my custom field in the list. I select it. But I found it is of type lookup. where as I want to that should be picklist. How to get picklist field of my custom entity field?

1:N relationships will always show up in CRM as lookups. N:N relationships will show as a separate grid on the left navigation of an entity. Without custom code, you can't get your lookup to appear as a picklist.