The Mali Empire (1240-1645 CE) of West Africa was founded by Sundiata Keita (r. 1230-1255 CE) following his victory over the kingdom of Sosso (c. 1180-1235 CE). Sundiata’s centralised government, diplomacy and well-trained army permitted a massive military expansion which would pave the way for a flourishing of the Mali Empire, making it the largest yet seen in Africa. The reign of Mansa Musa I (1312-1337 CE) saw the empire reach new heights in terms of territory controlled, cultural fluorescence, and the staggering wealth brought through Mali’s control of regional trade routes. Acting as a middle-trader between North Africa via the Sahara desert and the Niger River to the south, Mali exploited the traffic in gold, salt, copper, ivory, and slaves that crisscrossed West Africa. Muslim merchants were attracted to all this commercial activity, and they converted Mali rulers who in turn spread Islam via such noted centres of learning as Timbuktu. In contrast to cities like Niani (the capital), Djenne, and Gao, most of the rural Mali population remained farmers who clung to their traditional animist beliefs. The Mali Empire collapsed in the 1460s CE following civil wars, the opening up of trade routes elsewhere, and the rise of the neighbouring Songhai Empire, but it did continue to control a small part of the western empire into the 17th century CE.
The British Channel gave Britain a great advantage. At one point, the German Luftwaffe (air force) tried to invade the island, but the attempt failed and it was never attempted again
On the graph, you can see that after 1870-1919, Europe's immigration basically goes downhill. In that case, Europe received a very major decline in immigration, making it the right answer. Apologies if I'm wrong.
Let us choose Extra study. Knowing that opportunity cost is related to the opportunities lost by choosing one specific course of events than others. By choosing an extra study and spend hours studying something, my opportunity cost will be the school sports practice hours that could be spent in this time. Another opportunity cost would be the social interaction, in a club, for example, lost because of the extra study decision.
