How can you tell when a work of art has achieved a sense of unity? when elements are combined to promote visual interest when the art emphasizes a particular element when a viewer’s eyes follow a path or motion when the art gives a sense of harmony

I think it's a)

Elements combined together well-harmoniously in an artwork is considered unity. So, answer choice a is probably the most accurate when considering how/what makes a work of art achieve a sense of unity.

How can you tell when a work of art has achieved a sense of unity?

when the art gives a sense of harmony

they most likely have a instrumental version. just look it up on google.