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.
If there is a subject of really ______________ interest and utility, it is the art of writing and speaking one's own language ___________. It is the basis of culture, as we all know; but it is infinitely more _________ that, it is the basis of business. ___________ salesman can sell anything unless he can explain the merits of his goods in effective language, or can write ___________ advertisement equally effective, or present his ideas, and the facts, in a letter.