Hills are easier to climb than mountains. They are less steep and not as high. But, like a mountain, a hill will usually have an obvious summit, which is its highest point. According to the U.S. Geological Survey, there is no official difference between hills and mountains.
Because they have the most direct sunlight possible.
Answer:
C) when nuclear fusion begins in the core
Explanation:
- <u>The protostar is a main-sequence star that has a core temperature that exceeds abut 10 million K and is needed for the hydrogen to operate efficiently and the </u><u>length </u><u>of this process depends on nature and the stellar </u><u>mass</u><u>, as the huge massive star have a greater and bigger core and fusion takes fast.
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- A protostar is also called as primitive star and represents the earliest phases of the process of the stellar evolution and takes place after it leaves form the main sequence star.
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