Final answer:
The outeropping basement complex rocks cannot be observed in Central Shewa in Ethiopia, but they can be observed in other areas mentioned in the question.
Step-by-step explanation:
Based on the information provided, we cannot observe the outeropping basement complex rocks in Central Shewa in Ethiopia. The other options mentioned - Central Tigray, Assossa, and the Abbay gorge - do allow for the observation of these rocks. The basement complex rocks refer to the rocks that form the foundation of the Earth's crust and typically include granite, gneiss, and other metamorphic rocks.