I believe the answer would be C, burning fossil fuels. Oil and gas is made up of the remains of microscopic plankton. Over millions of years the remains become the carbon-rich coal, oil and gas we can use as fuel. When fossil fuels are burned they release carbon dioxide into the atmosphere, thus contributes to global warming.
They closed their borders and turned inward because they wanted to stop people from learning other religions. Two results are that they could no longer trade and they were confined to themselves.
T∅P
No, he was not a god, he was mortal.
March 21 1942 in Melbourne, Australia
