问题详情

When Charles Darwin explained evolution (进化) , the process he saw was natural selection
(选择) . It turns out human selection can also cause plants to evolve.
Take the case of the snow lotus, a rare(稀少的) plant that grows only high up in the Himala-yas. Researchers have discovered that one type of the plant has been becoming smaller over time
——the one people like to pick.
A type of snow lotus called Saussurea laniceps is used in Tibetan and Chinese medicine and is increasingly demanded by tourists. The largest plants are picked, and that occurs during their only
flowering period.
The result is that only smaller, unpicked plants go to seed. Selection caused by humans is a powerful force, according to some scientists. They studied the plants picked over time and also compared the snow lotuses growing in heavily harvested areas with those found in places where peo-ple rarely picked them.
They reported in an article that the heavily harvested snow lotuses have been getting shorter o-ver the last century, while those in areas not picked have remained the same. They found that in the heavily harvested areas, where only the smaller plants got to reproduce, the average height was 5.3 inches. The same plants in rarely harvested areas averaged 9 inches in height. And they noted that another type of snow lotuses which is not often picked, has not been changing.
69. What does the word " that" (line 3, para. 3) refer to？
[ A] Research done by Darwin.
[ B ] Seeds of Saussurea laniceps by natural selection.
[ C] The picking of Saussurea laniceps by tourists.
[ D ] The Saussurea laniceps used in traditional Chinese medicine.请帮忙给出正确答案和分析，谢谢！