17) is the use of a light source to create highlights and shadows.

There's a good reason why - outside of a nice piece of flat design - nobody looks at 2D colored images twice. Anybody can do that. A quick Google search will prove it and you'll even wonder why you wasted your time scrolling through the bad examples. On the flip side, adding shadows and highlights to your work is going to leave a seriously good impression. So, here's how shadows and highlights are key to making work look professional.

nothing certain is known about what happened, but it seems that the country declined gradually, perhaps due to bad government, or, more likely, due to a series of bad harvests, which resulted in widespread and recurrent famine.