Checkboxes
When a drop-down only has two answer options, or when you want to be able to select multiple options from a list, you can display them as checkboxes.
Drag the Checkbox answer type from the Toolbox into your form.
After selecting your question, choose an answer option. In the answer options stage, select which two answer options to include. You are unable to proceed if more than two are selected.
Checkboxes do not display answer labels so work best for Yes/No questions.
Checkboxes do not have a null option associated.