What does "the puzzle" (Line 1, Para. 4) refer to? A) The cause of the ice-age cycle. B)
What does "the puzzle" (Line 1, Para. 4) refer to? A) The cause of the ice-age cycle. B) The duration of an ice-age cycle. C) Whether the ice-age cycle is related to the changes in Earth's orbit. D) How fast the seas rose when the ice-age cycle was about to start.