Complex sentence: The enormous differences between the regions pose a serious structural problem for the Angolan economy, illustrated by the fact that about one third of economic activities are concentrated in Luanda and neighbouring Bengo province, while several areas of the interior suffer economic stagnation and even regression.
Split into simpler sentences: The enormous differences between the regions pose a serious structural problem in the Angolan economy. This is best illustrated by the fact that about one third of the economic activities is concentrated in Luanda and the neighbouring Bengo province, while several areas of the interior are characterized by stagnation and even regression.