If you have a form of "ten" in Polish, actually all three ([this/that/the]) work.
Well, 'this' is the direct translation. 'that' works, because 'that' is used a lot more often in English than its counterpart "tamten" in Polish. So in fact this/that/that = ten/ten/tamten.
Finally, why "the"? In fact often in English when you have "the dog", what you mean is almost the same as "this dog" and it would make a lot of sense to translate it into Polish as 'tego psa'.
But the main answer is always the direct equivalent, so here "this".
I found kinda bug in a polish-to-english translation exercise, I guess. First I had written "New people like that dog". Of course the system marked it wrong, but it underlined "people", not "like". So I was trying to check what was wrong with the "people" still typing the wrong word untill I actually saw where real mistake was