Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

Q: Exotic species are also called invasive species because they threaten other species.

A: Why are exotic species also called invasive species?
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Q: Starches are complex carbohydrates that are the polymers of glucose.

A: What complex carbohydrates are the polymers of glucose?
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Q: Saliva secretion initiates chemical digestion while also protecting the oral cavity.

A:
What secretion initiates chemical digestion while also protecting the oral cavity?
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