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.

Although it has been felt necessary to devote much space to ________ attempt to find principles that may be said to be at the basis ________ the art of all nations, the executive side of the question has not been neglected. And it is hoped that the __________ method for the study of drawing from the two opposite points of view of line and mass here advocated may be useful, and help students to avoid some of the _____________ that results from attempting simultaneously the study of these ______________ qualities of form expression.