Answer: A
Explanation:
Oxygen makes up another 20 to 21 percent of our atmosphere. It's essential for life on Earth, and interestingly enough, it is poisonous when highly concentrated. Our concentration of 20 to 21 percent seems just right.
The answer is true you are welcome
This statement is true: <span>The mineral ores for gold and silver are commonly found in the earth's crust.
These two types of metals are known as native metals because they are naturally occurring within the Earth's stratosphere. These metals are usually found through mining processes because they are often found mixed with sediments and other soil components. One method of acquiring gold is called gold panning while silver is obtained mixed with silver sulfide and sulfosalt minerals.</span>