Countries would be able to increase their productivity for the services with comparative advantage. A country then can sell products they produce efficiently and also would buy from other nations the products that they cannot produce. The comparative advantage can lose if there are competitors operating in a low wage country.
Answer:
C is correct answer because it is 10 billion.
If you mean geographically/biologically - the world is changing, and so will the environment, and with the problems we have now a days, it's likely to change fast in aspects such as temperature (will get hotter), fauna and flora (will decrease), etc.
If you mean politically - some countries might gain more territory trough battles or wars, and some other countries might possible "reclaim" long-lost lands that belong to them historycally.
Hope it helped,
BioTeacher101