Which makes bacterial infections difficult to defeat?
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a. bacteria live in viruses.
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b. bacteria live outside of cells.
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c. macrophages work slowly.
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d. killer t cells must attack host cells.

After which event could you say that evolution has occurred? question 1 options: an allele frequency changes in a population. a white-eyed fly is born into a population of brown-eyed flies. a new predator comes into an environment. an animal gets fat.

Ameadow ecosystem includes many species of grasses and small shrubs, several herbivores, and a few carnivores. a fungus colonizes the meadow and kills most of its vegetation. what is most likely to happen to the populations of herbivores and carnivores in the ecosystem? a. the populations of herbivores and carnivores will increase because there will be less competition for chemical energy. b. the populations of herbivores and carnivores will remain stable because the fungus cannot infect these organisms. c. the populations of herbivores will decrease because of vegetation loss, but the population of carnivores will remain stable. d. the populations of herbivores and carnivores will decline because less chemical energy will be stored in the ecosystem.

What materials must dams have to produce electricity, and what must occur?