Final answer:
The Akkadian Empire facilitated trade through the construction of The Royal Road and canal system (C), rather than through other significant structures like The Ziggurat of Ur or the possibly mythical Hanging Gardens of Babylon.
Step-by-step explanation:
The building project that helped trade in the Akkadian Empire is C) The Royal Road and canal system. The Akkadian Empire was known for its advancements in infrastructure that facilitated commerce and administration, and among these, the Royal Road and canals played a significant role in enabling movement of goods and people across the empire. While ziggurats such as The Ziggurat of Ur were crucial religious and administrative centers, they were not directly built for supporting trade. Likewise, the Hanging Gardens of Babylon, although architecturally significant, is attributed to later times and different rulers, specifically Nebuchadnezzar II, and there is much debate about their actual existence. Similarly, there is no historical evidence to support the existence of the Great Wall of Akkad.