What can be useful to highlight the main subject in a picture?

Correct answer: Contrast

The direct answer is A, Contrast. Contrast means a clear difference between parts of a picture, such as light and dark, large and small, warm and cool, or bright and dull. When the main subject looks different from its background, the viewer notices it first. Step by step: identify the main subject; compare it with the surrounding area; increase a useful difference in colour, tone, size, shape, or detail; then the subject becomes clearer and more prominent. Option A is correct because contrast creates emphasis and separates the subject from the background. Option B, paper fold, may change the surface or shape of paper, but it is not the normal visual method for highlighting a subject. Option C, a bell, is an object and its sound has no necessary role in arranging emphasis in a picture. Option D, only glue, is an adhesive and cannot by itself create visual emphasis. Remember: to make something stand out, make it visibly different from what surrounds it.