Passage 3

Questions 11 to 15 are based on the following passage.

There was once a tree in South Africa so wide that it could fit 60 people inside its hollow trunk. The tree reached 62 feet into the sky. It was more than 1,100 years old. But recently, that tree and others like it have died. （79） Scientists are wondering why.

The tree was a baobab. A baobab looks like a giant oak（橡树）turned upside down. It's branches resemble roots reaching toward the sky. It grows in Africa and is called the Tree of Life. Baobab trees tend to live a long time. One of the oldest stood fbr more than 2,400 years. Various baobabs have been used as a shop, a prison, a house, and a bus shelter.

In 2005, scientists began a survey to determine the age of more than 60 baobabs. （80） During the process, they noticed that several of the trees had died. Their results, recently published in Nature Plants, show that nine of the 13 oldest baobab trees and five out of six of the largest died in the 12-year study period.

Stephan Woodbome conducted the baobab study with six other scientists. They say more research is needed to know why the trees died, but they think climate change may be to blame. That's because the trees showed no evidence of disease. Plus, many were in national parks, so they would have been protected from human ham. Also, Woodbome says, the most affected baobabs are on the outer edge of their ideal habitat。西息、地）.Increasing heat and shifting rainy seasons have made it harder fbr baobabs in these areas to tlirive.

Smaller and younger baobabs are dying too. "The big ones and the old ones caught attention of the media,^,Woodbome says, "But ifs not just those. Ifs unprecedented （空前的）that they should be dying across the age spectrum. We've got to do a reality check on our own footprints in tenns of the way we live our lives. If we all changed what we did a little bit, it would start to make a difference.