Answer: industrial emissions and motor vehicles smokestacks fuel combustion
Explanation: All of these are anthropogenic causes of acid rain.
Hope this helps! :)
The mass number of an element is equivalent to the number of Protons and Neutrons in the element. For example Oxygen has eight protons and neutrons, therefore its mass number is 16. You could also calculate this by simply rounding the atomic weight of the element to the nearest whole number. Oxygen's atomic weight is 15.994, which as you can see, would be rounded to 16 :)
An estuary is where salt water and fresh water meet. Estuaries are usually found at the edge of the coast, where the ocean water, or salty water, meets river, lake, any fresh water source, water.
A tributary is something completely different. It is a, usually smaller than the main river or lake, river/stream stemming off a bigger river or lake, or flowing into that river or lake.
