From Twitter:
Jo: Trump passed a new law.
Bo: _. What is it, no Korean or Chinese travel?
Jo: I thought you didn’t care.
Bo: I don’t, but was I right?
Jo: No. He banned negative reporters from the White House.
Bo: Old news.
Choose the best answer:
I couldn’t care.
I don’t know.
Who cares?
Answer
The answer is Who cares, because this expression means no one cares, certainly I don’t care, so who does (care)?
‘I don’t know‘ doesn’t create any sense, if you look at the statement from Jo. It would not be the correct response.
I couldn’t is grammatically correct, but awkward without ‘less,’ as the common expression is ‘I couldn’t care less.’