Finish the following sentence with the best choice: How big should the entire shelf unit be when making easy cardboard shelves?

Choices:
- Each unit should be built at most 2 inches wide. The height can vary somewhat depending on your needs, but 42 inches high makes the it stable and sturdy.
- Each unit should be built at most 20 inches wide. The height can vary somewhat depending on your needs, but 42 inches high makes the it stable and sturdy.

Answer:
Each unit should be built at most 20 inches wide. The height can vary somewhat depending on your needs, but 42 inches high makes the it stable and sturdy.