Systematic observation, measurements and experiment and the formulation .testing.and modification of hypothesis
Explanation: Natural gas is a limited resource. Natural gas is in the fossil fuel family and it's underground. I think it's pretty plentiful meaning that there's a lot in the United States of America. Many people use it for home heating instead of heating oil. Some people have oil trucks where the oil truck has to come and deliver oil to them.
So, natural gas is limited resource because it's a fossil fuel and it gives off emissions. It's in the ground and it's from years of decaying stuff. It's not like solar or wind power, it's a limited resource.
Answer:
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Crossing over in which alleles are exchanged.
