Can I just select one option of a *Select Many*

You could do this as outlined in the image below:

In the survey tab of your xlsform:

In the choices tab of your xlsform:

Image 2

Data entry screen as seen in Enketo: when a wrong entry is made

Data entry screen as seen in Enketo: when a correct entry is made

Reference xlsform:

Dummy Questions.xls (26.5 KB)