|The main cause of climate change is:||b) orbital eccentricities of Earth and variations in the Sun's output|
That is correct, although you certainly won’t hear it from Al Gore or governments.
Climate change occurs in cycles caused mainly by changes in the Sun's output and the Sun's position relative to the Earth. Even the recent UN IPCC report attributes well over 50% percent of temperature change of the last 130 years to changes in just one band of the incoming of solar energy spectrum. This amount is now increased by the adjustment due to error recently discovered in the modern record. Long term the Milankovitch Effect (Sun/Earth relationships) explain approximately 75% of temperature change.