B．The carbon dioxide their bodies create.

C．The amount of their urine，sweat and breath.

D．The remaining isotopes in their body.

31．What is the purpose of Pontzer's study？

A．To confirm that an athlete's physical extreme is mainly determined by his BMR.

B．To compare human limits in common exercise with those in endurance activities.

C．To find out where the highest energy consumption of an athlete lies.

D．To set a reasonable standard for researches concerned with human body

32．How did Pontzer feel when their study results came out？

A．Excited. B．Regretful. C．Surprised. D．Hopeful.

D

“Give us back our stolen hour！” Britons demanded as they objected to the introduction of Daylight Saving Time（DST）in 1916. The idea of setting the clocks to move an hour of daylight from the morning to the evening during summer has been controversial（有争议的）throughout its history. People have argued that the practice saves energy, reduces crime, and prevents traffic accidents. Others are not so convinced, and studies conducted over the past decade have shown mixed results.

The idea was first put into operation in Germany during World War I（1914­1918）in an attempt to reduce coal supply during wartime. Britain soon followed with its own Summer Time but so did confusion and chaos, with some institutions following the changes and some simply ignoring them. One writer felt angry at the laws in a more poetic manner, expressing his dislike for being forced to favor the sun over the moon.

Despite the early controversy, 82 countries currently use DST. The United States moves its