Поставьте предлог где необходимо 1)what do you think _ great britain? 2) countries _ the world are different _ their size 3) america consists _ north america and south america 4) i started school _ the age of seven 5) the computer classes are located _ the finest floor

1)what do you think of/about Great Britain?
2) countries of the world are different in their size
3) America consists in  north America and South America
4) I started school in/at the age of seven
5) the computer classes are located at the finest floor