"o" doesn't change, it remains the same :) Some people would use "od", but I'd say it's pretty "odd" B) Jokes apart, the truth is that it isn't wrong, but it's very rare and it's basically disappearing. If you use it, it'll sound strange to most people, though someone will surely come here to say that it's the most rightful way of saying it ;)
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Has difficulty understanding even short answers in this language.
Can ask simple questions and can understand simple answers.
Can ask all types of general questions and can understand longer answers.
Can understand long, complex answers.
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