A continent is a large land mass and its surrounding shallow continental shelf. Both are composed primarily of <em>granite</em>, which is lighter than the liquid mantle of the Earth and therefore floats upon it like cork on water.
Granite would be the correct answer but i see you don't have that there, Lithosphere i would say may be the right answer. or this
The continents are made out of relatively brittle rock called the "Crust"
Answer - They take in C02 (Carbon Dioxide) & Release O2 (Oxygen)
Reasoning - To be able to do Photosynthesis they Plants need C02 which is one of the important components to making Glucose. During that gas exchange they release O2 for C02.