Here's a normal 'choice' task and Mom's usual answer:
'Mom, do you want to have steak or fish for dinner?'
'humm, I don't know, let's have both!'
It happens all the time, so there are things that I don't allow her to try to do, things like ordering food out, and clothes to wear, I just do it for her. I know people think that I'm not such a nice guy when I do it, but I've been living inside the confusion of Mom's dementia for so long....its my little coping mechanism!