How do I make it compulsory to complete all fields in an ezine sign-up form?

See my form here.

If you try to fill in the form, you will see that it lets you complete the procedure without filling in all the sections (no name, and for many subscribers the country value="Select Country" ).

Is there anyway to make it obligatory for somebody to fill in all the fields? How can we make all the fields, including name and country, compulsory?

Thank you very much for your help. I appreciate you taking the time to advise me