What are positive shapes?

A.

the shapes of artists' canvases

B.

the main shapes in a painting

C.

the automatic shapes created for backgrounds

B, the main shapes in a painting

Explanation:

Positive shapes are the shape of the actual object (like a window frame). Negative shapes are the spaces in between objects (like the space within the window frame)

B.

It is the main part of the painting that shape the actual object