The U.S. wanted to prevent the spread of communism.
Answer:
Their movement is driven by heat within the Earth. ... This causes hot material within the Earth to rise, until it reaches the surface where it moves sideways, cools, then sinks. This circular motion is called convection. Convection within the mantle drives the motion of the overlying plates.
Answer:
ponds cooler than 20 °C
Explanation:
There is great effect of temperature on the dissolved oxygen in a pond water,
When the water is hotter it will hold less oxygen but when the water is cold it will holds more oxygen. Therefore, ponds cooler than 20 °C will will have a higher average oxygen concentration.
Ozone layer depletion was not noticed until 1979, while CFC’s have been around since 1920s because CFCs take time to enter the stratosphere and remain there for at least 60 years after their initial release.
Option: A
Explanation:
Ozone layer is found in stratosphere. Ozone plays a dual role in the environment. When it is in the ground surface zone it is a harmful gas but when its in the atmosphere it is a life saving layer which absorbs UV rays and protect human beings and animals from the harmful affect of poisonous gases.
Though ozone layer started depleting from 1920. But it came into notice from 1979 as CFCs take time to enter the stratosphere and remain there for at least 60 years after their initial release.
They can divide the region by making it harder to move, like mountains and water.
