I had to look this up, and it appears that "de" is pronounce more like "dee" would be in English, and "det" is pronounced closer to "day". Both sound a touch flatter to me than they would in English.
Hope that helps! (And I hope I'm right, too.)
Is there a reason not to accept "This is your elephant" - Only It, and That are accepted - I reported it, but maybe I was just wrong :)
When you rougly translate the two words "this" would be "dette" and "it" would be "det". So I think it's for a more simple sentence. I think both should be accepted. Not sure though ;)
I would say in Danish there is no difference between 'this' and 'that' and I would agree they should both be accepted. Den and Det only relates to the noun's form in 'ubestemt' , that is, if it has an 'en' or 'et' in the regular form (not sure what bestemt and ubestemt translates to English)...
Could this also be "THAT is your elephant" ... As well as "IT is your elephant?"