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 ___(11)___ their guard”. The report also says it is essential, “to develop a more comprehensive understanding of how different species in different situations ___(12)___ to human visitation, and under what precise conditions human exposure might put them at risk".