The right answer is 4: Asia, Africa, Antarctica and Australia.

A continent is one of several very large landmasses. Generally identified by convention rather than any strict criteria, up to seven regions are commonly regarded as continents. Ordered from largest in area to smallest, these seven regions are: Asia, Africa, North America, South America, Antarctica, Europe, and Australia.

Geologically, the continents correspond to areas of continental crust that are found on the continental plates, but include continental fragments such as Madagascar that are not commonly referred to as continents. Continental crust is only known to exist on Earth.

More Info: en.wikipedia.org