Make checkboxes to be marked by default

I want to have a question where there are two options and the user needs to select one but instead of having the boxes blank, I want them them both to be checked (marked with a V) so that the respondent has to un-check one of the options so that the option he preferred remains checked.
Is that possible? Any suggestions?
Thanks! Eyal.

Hi Eyal, yes, but only with a custom item. I know with HTML checkboxes, you can set the default to be checked instead of the default unchecked. Is that doable for you?

Thanks, Blair. I guess I could learn how to do it but I was actually hoping you'll gave some template that I can start from.
Eyal