英语首字母填空题目air is everywhere around us．hot air is very （l ）．an

英语首字母填空题目
air is everywhere around us．hot air is very （l ）．and some early （b ）used hot air．you have seen hot （s ）rising overa fire．the hot air takes it up．some ballons carried the fires under them,then they took up （i ）the sky．it was not a （s ）from of travel．