JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
You may want to try the multiple selection widget instead of using the standard Drop Down field. You can check this link for more information regarding the widget: http://widgets.jotform.com/widget/multiple_selection. You can also check this demo form for sample implementation of the widget: http://form.jotformpro.com/form/43452693159967.
Do let us know if you need further assistance.