Scientists hypothesize that oxygen began to accumulate in Earth’s atmosphere after the appearance of living things with the ability to

amber has allowed scientists to study dna that has been preserved over millions of years.

after receiving a stimus, the sensory receptors send(s) signals to the appropriate area of the body.  

the must be sensory neurons.  

hope its .

the correct answer, according to e2020, is the second choice there is an occluded front in region a and a cold front in region b.

1. efficient use of space

2. elimination of groundwater contamination

3. energy generation

4. lower carbon footprint