Lets take a look in each proposition:
Britain did more than abolish slavery, it took robust action against the slave traders and strongly encouraged others to do the same. As we can see, the empire that abolish slavery was United Kingdom not Portuguese empire.
Exploitation and oppression was an essential part of colonialism and was also part of the Portuguese Empire. They looked at indigenous cultures and religions with disdain and superiority. The overall result was genocide and the consequent appropriation of indigenous land. As a result, Many indigenous cultures lost their land is a correct proposition.
The Portuguese empire was one of the largest and longest-lived empires in world history and existed for almost six centuries. Given Portugal size and population we can affirm that a small country can make a big impact.
Portuguese empire last from 1415 with the conquest of Ceuta until 1999 with the handover of Macau, China. Even representing almost six centuries the European imperialism was not ended with the end of Portuguese empire. Even today we still have contries as United Kingdom, France and Netherlands with territories outside Europe.
Which gives us, B and C as correct.
