<span>Scientists choose where are units of time began and ended based on major changes in life forms at certain times</span>
Letter B. global winds and pressure systems
Answer:
growth rate will be 4.5 %
So option A is correct option
Explanation:
We have given immigration = 50
Emigration = 20
Birth rate = 25
Death rate = 10
Each per 1000 people
We have to find the percentage growth rate of this country
Percentage growth is given by immigration - emigration + birth rate - death rate
So percentage growth rate = 
%
So growth rate will be 4.5 %
So option A is correct option
Currents involve movement of ocean water masses, driven either by wind or by differences in temperature, salinity and density. The most important from a human perspective are the wind-driven surface currents that move water in the uppermost layer of the ocean.
Currents affect humans in several primary ways. Currents help shape the climate in the areas where we live, create the right conditions to support abundant ocean life in the areas where we fish, and change weather patterns through periodic events like El Nino/La Nina.
Ocean currents also cause upwelling in many areas like off in the inland parts of North America, where surface currents taking water away from the shore cause nutrient-rich water to well up from the ocean deeps. The abundance of nutrients in these areas forms fertile ground for kelp beds and marine fisheries, which in turn furnish food for humans. Alterations in current patterns like the El Nino/La Nina cycle affect humans as well by causing changes in local weather patterns in the years when they occur.
