B. Ozone. It's Ozone because thermo in the word thermosphere means heat. The word sphere means the shape, which is the shape of Earth, and you're asking for the most of the presence, which only means in earth, that's why I pick B.
Kharif crops are grown in the begging of “rainy season” (April & May). Rabi crops are grown at the beginning of winter or between September and October.
