A common mistake we often see people making on their forms is the use of checkboxes instead of radio buttons. If you are asking a yes/no question or any question where you only want one answer, you should never use a checkbox field. The reason for this being that a checkbox field will allow a user to check both “yes” and “no” on your form. A radio button, on the other hand, forces the user to choose only a single response, “yes” or “no”.
By default, select lists also only allow a user to choose one item from the list. However, there is a trick to allow users to select more than one item from a select list if you so wish. The way to do this is to change the field size of the select list to display more than 1 row.
If you set the number of rows to 2 or greater, you will be able to choose multiple answers from a select list.