Here is the method to create this....
Create (drag over) two text fields, use different Data Labels, perhaps the first is called "Corporation TaxID and the other "Partnership TaxID". Create conditional rules starting by highlighting the Radio Button for Corporation, the rule should show "Corporation" in the dropdown then you hold down CTRL key and select Text field 1 that was labeled as Corporation Tax ID. Save or Done. Highlight Radio Button for "Partnership" and again select "Create Rule" select "Partnership" from the dropdown and then CTRL and highlight text field labeled as "Partnership TaxID". Save or Done. Now take these two Text fields created in the first steps and place them right on top of each other in the appropriate location. So they are in essence stacked conditional fields. If the Recipient chooses the Partnership option or the Corporation option it will show a text field to fill out.