Read the following passage carefully and answer the question by choosing the most appropriate option from the given choice.

(1) The atmosphere is a mixture of several gases. There are about ten chemical elements, which remain permanently in gaseous form in the atmosphere under all natural conditions. Of these permanent gases, oxygen makes up about 21 per cent and nitrogen about 78 per cent. Several other gases, such as argon, carbondioxide, hydrogen, neon, krypton and xenon, comprise the remaining one per cent of the volume of dry air. The amount of water vapour and its variations in amount and distribution is of extraordinary importance in weather changes. Atmospheric gases hold in suspension great quantities of dust, pollen, smoke, and other impurities which are always present in considerable but variable amounts.

The atmosphere has three well defined strata.

(2) The layer of the air next to the earth, which extends upward for about ten miles is known as the troposphere. On the whole, it makes up about 75 per cent of all the weight of the atmosphere. It is the warmest part of the atmosphere because most of the solar radiation is absorbed by the earth's surface which warms the air immediately surrounding it. A steady decrease of temperature with increasing elevation is a most striking characteristic. The upper layers are colder because of their greater distance from the Earth's surface and rapid radiation of heat into space.

(3) Above the troposphere, to a height of about 50 miles, is a zone called Stratosphere. The stratosphere is separated from the troposphere by a zone of uniform temperatures called the tropopause. Within the lower portions of the stratosphere is a layer of ozone gases which filters out most of the ultraviolet rays from the sun. The ozone layer varies with air pressure. If this zone was not there, the full blast of sun's ultraviolet light would burn our skin, blind our eyes and eventually result in our destruction. Within the stratosphere, the temperature and atmospheric composition are relatively uniform.