Converting carbon dioxide to carbon monoxide through reduction would be effective method for reducing harmful levels of atmospheric carbon dioxide. However, this conversion is very difficult for which of the following reasons?

W) There is a limited supply of rhenium in the world

X) Not all steps of the reduction have been completely determined

Y) The final step takes an extremely long time

Z) The carbon dioxide is too difficult to harness
W) THERE IS A LIMITED SUPPLY OF RHENIUM IN THE WORLD