Rainwater contains hydrogen of a heavy form called deuterium. The deuterium content of wood reflects the deuterium content of rainwater available to trees during their growth. Wood from trees that grew between 16,000 and 24,000 years ago in North America contains significantly more deuterium than wood from trees growing today. But water trapped in several North American caves that formed during that same early period contains significantly less deuterium than rainwater in North America today.
Which of the following, if true, most helps to reconcile the two findings?
A) There is little deuterium in the North American caves other than the deuterium in the water trapped there.

B) Exposure to water after a tree has died does not change the deuterium content of the wood.

C) Industrialization in North America over the past 100 years has altered the deuterium content of rain.

D) Trees draw on shallow groundwater from rain that falls during their growth, whereas water trapped in caves may have fallen as rainwater thousands of years before the caves formed.

E) Wood with high deuterium content is no more likely to remain preserved for long periods than is wood with a low deuterium content.