All of the following are important elements to projecting an idea to a concrete work of art, except which?
a. balance
c. metaphor
b. design
d. symmetry

The important elements of projecting an idea to a concrete work of art are balance, design and symmetry. All these three are very important to be able to create a concrete work of art. Thus, the one which is not part of it is the metaphor.

Explanation:

The asymmetrical construction resembles to be durable and produces a more neat look. You can see a prominent example of this in the picture above. The one on the license uses the same shapes in the same colors and balances them asymmetrically. Both sides are complex, yet ordered in such a way that they feel balanced.