阅读下列短文，从每题所给的四个选项(A. B. C和D)中，选出最佳选项。
At least 10 million hectares of cultivated（耕作）land in China are polluted, which makes a grave threat to the country’s food safety, the Xinhua News Agency reported on Friday.
The polluted land，which is mostly in economically developed areas，accounts for one-tenth of the country’s total arable（可耕种的）land，according to an incomplete survey by the State Environmental Protection Administration，China’s top environment watchdog.
Pollution on cultivated land threatens the environment，food safety and the sustainable development of agriculture，the administration said.
Because of continual，too much use of chemical fertilizer, pesticide and agricultural plastic sheeting, as well as irrigation using polluted water, a large amount of contaminants（污染物）remain in the cultivated land.
The contaminants affect the soil’s ecological structure and function，leading to decreased soil productivity, lower crop yield（产量），and lower quality of agricultural products-
It also leads to worse water quality in rural areas.
Less than 9 per cent of drinkable water passed checks for bacteria in243 rural water supply stations across the county.
Another survey, which took samples of drinking water and groundwater an 69 small towns。 in Beijing, Tianjin and Hebei Province of North，China, showed that more than half of the water contains too much nitrate（硝酸盐），which may cause diabetes（糖尿病）and damage the kidney.
The administration estimated at least 1 90 million farmers are drinking water that contains harmful substances.
Many villagers drink unfiltered water taken from shallow water wells or water cellars， which are reported to have poor sanitary conditions·
68. The author writes the passage to .
A. 1et the readers examine their mistakes
B. present the readers a new idea
C. come up with a solution to ending farmland pollution
D. inform the readers of the importance of fighting farmland pollution
69. The underlined word “grave” in Paragraph 1 probably means
A. serious B. certain C. big D. terrible
70. Pollution on cultivated land leads to the following outcomes EXCEPT .
A. a threat to China’s food safety
B. worse water quality in rural areas
C. a variety of diseases
D. the sustainable development of agriculture
知识点：科普环保类阅读
DAD