请先阅读下面短文,掌握其大意,然后从各小题所给的A、B、C、D四个选项中选出可以填入相应空白处的最佳选项。A team of Chinese scientists have found a new giant sinkhole (天坑). It's 192 meters 1 . What did they find at the 2 ? An ancient forest!
This 3 discovery was found in Leye County, in Guangxi Zhuang autonomous region. Leye County is known 4 "the museum of sinkholes". People have 5 about 30 sinkholes there so far.
How do sinkholes form?
China has a karst landscape (喀斯特地貌), Veni told Live Science. Karst landscapes are made when rainwater runs through little cracks (裂缝) in the 6 . The cracks 7 grow into tunnels (隧道) and then big caves (洞穴). Over time, a cave can get too 8 . Its ceiling then falls slowly, opening up huge sinkholes.
Veni called China's sinkholes "spectacular (壮观的)" because of 9 great sizes.
10 are sinkholes important?
Besides looking cool, karst caves and sinkholes can be the 11 to all kinds of plants, animals and microbe life (微生物). The newly discovered one has ancient trees up to 40 meters tall. "I wouldn't be surprised to know that some species (物种) in these caves have never been 12 or described by science until now," said the leader of exploration team, Chen Lixin. This is 13 the sinkholes are separate from the outside world. That 14 an environment for new species to form.
Sinkholes also have deep stores of underground water. They are like nature's water pipes (管道). They bring 15 to 700 million people worldwide, Veni told Live Science.