hey you didnt put usa on the poll. 
Did it ever occur to you that there is no continent "usa" ?
In geography you learn that there are three big platters of earth, one called the eurasian continent (despite africa being there too), the second one being america, and the third one being australia. Aside from these there are only relatively small pieces of earth so they're put along one of the big ones.
These earth-pieces are then broken into more or less equally sized blocks. Eurasia is broken into Europe, Asia and Africa, America is broken into North-America and South-America (how original), and Australia is left alone.
Then you split those pieces up into countries, and one of those insignificant countries that happens to be on the North-American bit is called USA.
Note that you are less than 1/10th of the earth's surface, and less than 1/10th of the earth's population.
