黃金閱讀TPO 13 - 英檢

想請問大家 有關TPO13的第二篇Biological Clocks的插入題(13)


Because the internal signals that regulate waking and going
to sleep tend to align themselves with these external cues,
the external clock appears to dominate the internal clock.



Because the internal signals that regulate waking and going to sleep tend to align themselves with these external cues, the external clock appears to dominate the in nal clock.
Animals need natural periodic signals like sunrise to maintain a cycle
whose period is precisely 24 hours. ■Such an external cue not only
coordinates an animal's daily rhythms with particular features of the
local solar day but also—because it normally does so day after day-seems
to keep the internal clock's period close to that of Earth's rotation.
■Yet despite this synchronization of the period of the internal cycle,
the animal's timer itself continues to have its own genetically built-in
period close to, but different from, 24 hours.
■Without the external cue, the difference accumulates and so the
internally regulated activities of the biological day drift continuously,
like the tides, in relation to the solar day. ■This drift has been
studied extensively in many animals and in biological activities ranging
from the hatching of fruit fly eggs to wheel running by squirrels.
Light has a predominating influence in setting the clock.
Even a fifteen-minute burst of light in otherwise sustained
darkness can reset an animal's circadian rhythm. Normally,
internal rhythms are kept in step by regular environmental cycles.
For instance, if a homing pigeon is to navigate with its Sun compass,
its clock must be properly set by cues provided by the daylight/darkness
cycle.

為什麼是插入第3個方格 我寫第二個



還有第14題

為什麼第一個選項是主旨呀!!
Most animals survive and reproduce successfully
without coordinating their activities to external environmental rhythms.

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