Before the rise of the nation-state, european could be described as a continent
a. ruled by barbarian tribes
b. with an identity crisis
c. on the verge of collapse
d. of multiethnic empires

When a lake, river or other aquatic  system  becomes  eutrophic, it can have serious negative effects on other organisms like fish, birds and even people.if an algal bloom is so bad that it causes wide-spread death  in  the  water, the organisms that die will all sink to the bottom and start to decompose.

Answer(apex)  ok i looked up two diff, sites both say the answer is a technological innovation that has allowed people to adapt to living in hot climates, plz check first good luck///