In the following passage, some of the words have been left out. Read the passage carefully and select the correct answer for the given blank out of the four alternatives.

Let us examine the facts in the case more ____________. First of all, language is no more ____________ a medium; it is like air to the creatures of the land or water to fishes. If it is perfectly clear and pure, we do not notice it any more than we notice pure air when the sun is shining ________ a clear sky, or the taste of pure cool water when we drink a glass __________ a hot day. Unless the sun is shining, there is no brightness; unless the water is cool, there is __________ refreshment.