问题详情

By “just the tip of the iceberg” (Line 2, Para. 8), Siegel suggests that _________.
A．half-brain sleep has something to do with icy weather
B．the mystery of half-brain sleep is close to being solved
C．most birds living in cold regions tend to be half sleepers
D．half-brain sleep is a phenomenon that could exist among other species请帮忙给出正确答案和分析，谢谢！