While the official Correct answer is not bad English, "Please boil/cook the/some potatoes for me" means the same thing, as many have already pointed out, and should have been accepted by now, but it is still marked wrong.

What is wrong with "Please cook the potatoes for me"

Where does "some" comes from?
Other exercises indicate that "some potatoes" would be Genitive картошки. and that the correct translation here is "the potatoes". In particular, there is:
Купи картошки и свари её.
where genitive is used to say "Buy some potatoes"

A moderator really needs to address this issue.

Why can't this be "a potato"?