The seas on Saturn's Moon, Titan, are mostly composed out of methane, a liquid methane to be more specific. The methane is in liquid form because of the conditions on the moon, where it is very cold, which turns the methane into a liquid state, instead of the gas state as we have it here on Earth. The seas on Titan, compared with the seas on the Earth, are not big seas, more like small and medium sized seas, but the amount of liquid they contain in them is very big, and they can easily fill the biggest lakes on our planets with it.
C. 6.81x10^-4 It is negative 4 because the 6 is 4 digits away from the first 0. Scientific notation has one number and then the decimal place so it can not be A or E.