There is no much important of earth crust in human beings but for the people who r trying to be the scientist or discovers need to learn about it
The first one, valleys. Rivers had to be built over, no one wanted their farms to be turned into a railroad (or at least those with common sense), and deserts had no water and was really hot during the day and cold at night.
Tertiary
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1. A- the economy faced serious challenges
2. B- Modernized
