Well yes, but the only country is Australia itself; Australia is not only a continent, but is a country as well
The only country in Australia is Australia. There are no other countries in Australia.
There is only Australia, no other countries.
Australia, while being a continent, is also a country. It is not a collection of countries, just one. So the list of countries for Australia is; Australia.
There are no countries in Antarctica, and Australia is a country itself.
Australia
Australia is a single country. There are no countries on the Antarctic continent.
Australia is surrounded by sea, not by any countries
There are no countries within Australia, Australia is both a country and a continent.
Australia is the only country on the continent of Australia.
South Australia is a state within the country of Australia. It does not contain any countries.
South Australia is a state in its own right, and it is part of the country of Australia. There are no other countries in South Australia or any of the other states of Australia.
There are no countries IN Australia. Austria is both a continent and a single country.