I've suggested a few times already that part of this problem might be that asking questions is the first privilege you get and you get it for free.
If it costs something people would be more careful.
The cost can be anything:
- Classify 5 answers correctly
- Pick answers from a multiple choice
- Pay a dollar
- Wait a few days to activate
- etc
Ideally the user should be able to choose a method that suits them but make the account worth something.
As long as accounts are free, activate instantly and comes with a free right to ask questions, stop being surprised that new accounts pop up to ask silly questions.