Read the following passage and mark the letter A, B, C, or D to indicate the correct word that best fits each of the numbered blanks

Ecotourism is booming and many tour operators say this is helpful to nature. Every year, millions of people visit protected (1) ____ areas to observe rare species. However, a new report casts doubt (2) ____ this form of tourism. The report, (3) ____ in the journal "Trends in Ecology and Evolution", suggests that ecotourism damages more than (4) ____ nature. Researchers believe tourists disrupt animals in their natural (5) ____. They point to a recent (6) ____ in Costa Rica where turtles had problems laying their eggs because of the many tourists who had gathered (7) ____  the beach to watch them.

The report says that ecotourism is (8) ____ animals bolder. A human presence makes animals tamer and less (9) ____ about other animals. This could put them at (10) ____ of being attacked by their natural predators, so more of them will be killed. The report says that when animals interact with humans, "they may let down their guard”. The report also says it is essential, “to develop a more comprehensive understanding of how different species in different situations respond to human visitation, and under what precise conditions human exposure might put them at risk".

(1) ___________

• A. 
  nature
• B. 
  natural
• C. 
  naturally
• D. 
  naturism