Which of the Following Statements Does Not Lend Support to the Idea

Which of the following statements does not lend support to the idea that carbon dioxide is a cause of global warming?

A) Isotope ratios in atmospheric carbon dioxide show that much of the carbon dioxide in Earth's atmosphere today comes from the burning of fossil fuels.
B) We understand the physical mechanism of the greenhouse effect, by which carbon dioxide increases cause an increase in the planet's temperature.
C) Models of Earth's climate that include recent increases in carbon dioxide concentration match the observed temperature increases better than those that do not include it.
D) Models of the greenhouse effect successfully predict the actual temperatures of Mars and Venus from their atmospheric carbon dioxide amounts.