The right answer is B.population, lack of resources and poor leadership.
The empire of Portugal was one of the largest empire on Earth with bases in North and South America, Africa, and various regions of Asia and Oceania. Besides it size, Portugal population was very small and was unable to defend its own trade posts around the world. During the Napoleonic wars, the Portuguese court moved to its most prosperous colony, Brazil. But by this time, the empire was facing an economic crisis, agriculture disorganization, cities destroyed by conflicts with the French and Portuguese manufactures could not compete with the English. Pointed by many, as the result of lack of leadership.