The correct answer is - cyanobacteria.
The atmospheric oxygen came from the cyanobacteria. These were one of the earliest living organisms on Earth. The cyanobacteria was using photosynthesis in order to create its own food. The photosynthesis process requires sunlight, carbon dioxide, water, and oxygen. The oxygen is mostly released as a waste product from the process of photosynthesis, thus the cyanobacteria were literally releasing oxygen that was ending up into the atmosphere. As more and more cyanobacteria there were across the planet, more and more oxygen they were releasing into the atmosphere, slowly changing the composition of the atmosphere, and setting the basis of it as we know it now.
Answer: B - help map the ocean floor
Explanation: GPS which is an acronym for Global Positioning System is a global satellite based location and navigation system owned by the US Government. It was first used by the US Air Force in 1978. It's main purpose is to show a GPS user location and time information from anywhere on earth, where there is an unobstructed line of sight from the precise location to 4 or more GPS satellites. GPS is commonly used on land (obviously through every day use like when you use an uber) and in the air (pilots use GPS signals when they fly).
GPS can be used to track pets if there's a tracking device on their collars.
GPS is also used in taxis and can be used to track a cab after a hurricane.
Ordinary people can use GPS to collect information for scientists - an example of this would be taking a new undefined route on Google maps therefore adding to their archive of known routes/areas.
However GPS signals cannot penetrate water - sea water especially. Hence the answer is B
The answer to your question is,
Two. The twin towers both collapsed.
-Mabel <3
I think that a) is chemical, and b) would be chemical
