Answer:
Carbon dioxide
Explanation:
The carbon combines with oxygen to form carbon dioxide (CO2) and is released back into the atmosphere as a waste product when animals breathe and exhale.
You would add H+ ions if you added an acid. Thus lowering the pH.
Human being, teeth doctors and tools
Creeping thistle continuously survives through easy germination of seeds. The Creeping thistle seed can be buried in undisturbed soil for over 20 years and still become growable. And also, the roots help in their growth. They absorb nutrients and regenerate to form new plants. Although the roots may be able to penetrate some meters down, most regeneration occurs within or just below the plow layer. Portions of the adjacent roots become thick due to the developing storage tissue which is where new shoots are formed.
It is because that's a place where no one lives so they're safe.
