Solar flares occur constantly, and would have to be HUGE to impact the Earth's climate (remember, climate is measured over long periods of time). While solar flares do affect weather and other things, such as radio waves, they don't affect climate. So C is out. Variations in Earth's orbit are short-lived, so A is out. Earth's reflectivity would need to change in order to contribute to climate change, so ignore answer B.
Now let's look at D and E. Ocean circulation is one of the most important factors affecting Earth's climate, and the primary factor leading to changes in ocean circulation is plate tectonics, or, more specifically, continental drift due to plate tectonics. Plate tectonics cause continental drift, which changes ocean currents, which leads to ice ages, ice cap melting, and global climate change. D and E are correct.
I believe the answer is c
