27. What's the purpose of Paragraph 3?

A. To explore the biology of human brains.

B. To explain why people get cancer.

C. To analyse how placebos work.

D. To question Mr Wright's story.

28. What does Dr Anne Harrington think of the placebo effect?

A. It is limited.

B. It is effective.

C. It can cheat patients.

D. It goes against science.

President Barack Obama renamed North America's tallest mountain this week. For almost 100 years, the 20,310-foot Alaskan peak has been identified on most maps as Mount McKinley. Its name is now officially Denali.

This "new" official name isn't really new at all. Obama changed the mountain's name to Denali because, for generations, that's what people in Alaska have called it. The Athabascan people, a Native Alaskan group, named the peak Denali long ago. It means "high one" or "great one."

"We are officially renaming the mountain Denali in recognition of the traditions of Alaska Natives and the strong support of the people of Alaska," said U.S. Interior Secretary Sally Jewell.

Alaska Senator Lisa Murkowski praised Obama's move. "I'd like to thank the president for working with us to achieve this significant change to show honor, respect, and gratitude to the Athabascan people of Alaska," she said.

The name Mount McKinley got its start in 1896. At that time, there was a gold rush going on in Alaska. A gold prospector (勘探者) wanted to honor William McKinley of Ohio, who had just been nominated (提名) to run for U.S. president. McKinley would go on to become the nation's 25th president. He was killed in 1901,