Which of the following is true about global warming?

A) Temperature rates do not fluctuate because of any predictable cyclical events, so it is hard to tell if a change that is being observed is going to be long or short in duration.
B) According to National Aeronautics and Space Administration (NASA) scientists, the temperature on Earth has increased by about 1.4 degrees Fahrenheit since 1880.
C) Daily temperatures where people live fluctuate several degrees a day, so a 1-degree change in the earth's overall temperature is not something to be overly concerned about.
D) A ten-degree drop was enough to bury a large part of North America under a towering mass of ice 20,000 years ago.