Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer for each of the blanks.

     Scientists believe they now have scientific evidence to prove that ecosystems work better when there is a greater variety of species within them. This biodiversity is being lost destroying natural mechanisms that could repair the damage caused by man. 

     Findings show that losing plants and animals is not only reducing our quality of life but actually endangering our very existence. We cut down rich rainforests and replace them with one species plantations, such as pine and eucalyptus. We plough up meadows rich in different grasses and herbs and replace them with one grass, for instance rye or wheat. 

     When a natural ecosystem is simplified the basic processes in the ecosystem are altered and even damaged. Without their biodiversity, they are not able to serve as the natural cleaners of our planet. No longer are they able to absorb the carbon dioxide that is being produced in excess. The result is global warming, caused by the increase in the 'greenhouse effect', and ultimately, or even sooner, there will be a change in the world's climate.

Which of the following is not a species used to replace a rich ecosystem?