The findings add weight to the theory that large areas of the Amazon have recovered so well from past periods of agricultural use that the regrowth has been mistaken by generations of biologists for “virgin” forest.

　　During the past decade, researchers have discovered hundreds of large earth works deep in the jungle. They are up to 20 meters high and cover up to a square kilometer. Glaser claims that these earth works, built between AD 400 and 1400, were at the heart of urban civilizations. Now it seems the richness of the Terra Preta soils may explain how such civilizations managed to feed themselves.

　　11. We learn from the passage that the traditional view of slash-and-burn farming is that ________.

　　A) it does no harm to the topsoil of the rainforest

　　B) it destroys rainforest soils

　　C) it helps improve rainforest soils

　　D) it diminishes the organic matter in rainforest soils

　　12. Most rainforest soils are thin and poor because ________.

　　A) the composition of the topsoil is rather unstable

　　B) black carbon is washed away by heavy rains

　　C) organic matter is quickly lost due to heat and rain

　　D) long-term farming has exhausted the ingredients essential to plant growth

　　13. Glaser made his discovery by ________.

　　A) studying patches of fertile soils in the central Amazon

　　B) examining pottery left over by ancient civilizations

　　C) test-burning patches of trees in the central Amazon

　　D) radiocarbon-dating ingredients contained in forest soils

　　14. What does Glaser say about the regrowth of rainforests?

　　A) They take centuries to regrow after being burnt.

　　B) They cannot recover unless the vegetation is burnt completely.

　　C) Their regrowth will be hampered by human habitation.

　　D) They can recover easily after slash-and-burn farming.

　　15. From the passage it can be inferred that ________.

　　A) human activities will do grave damage to rainforests

　　B) Amazon rainforest soils used to be the richest in the world

　　C) farming is responsible for the destruction of the Amazon rainforests

　　D) there once existed an urban civilization in the Amazon rainforests