What 4 elements did people originally think made up everything?

The agent of mechanical weathering in which rock is worn away by the grinding action of other rock particles is call

If e is the symbol for an element, which two of the following symbols represent isotopes of the same element? 1. e2. e3. ea.1 and 2c.1 and 4b.3 and 4d.2 and 3

How is the use of hydroelectric power related to the sun