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.

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

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)