The art of using and understanding space involves __ a. varying the size of objects or subjects so that some are smaller than others and the illusion of depth is created. b. showing a change from light to dark in an object by darkening areas that would have a shadow. c. placing part of one shape or form in front of another. d. all of the above.

# Explanation:<br />## Step 1<br />The question is about the art of using and understanding space in visual arts. This involves various techniques to create depth and perspective in a two-dimensional artwork.<br /><br />## Step 2<br />Option a refers to the technique of varying the size of objects or subjects so that some are smaller than others. This creates an illusion of depth, as objects that are farther away appear smaller than those that are closer.<br /><br />## Step 3<br />Option b refers to the technique of showing a change from light to dark in an object by darkening areas that would have a shadow. This is known as shading and it helps to create a three-dimensional effect on a two-dimensional surface.<br /><br />## Step 4<br />Option c refers to the technique of placing part of one shape or form in front of another. This is known as overlapping and it helps to create a sense of depth by making one object appear in front of another.<br /><br />## Step 5<br />Option d states "all of the above", which means the techniques mentioned in options a, b, and c.<br /><br /># AnswerThe is 'd'. All the techniques mentioned in options a, b, and c are used in the art of using and understanding space in visual arts.