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Work is not done when you carry an object forward. You may have learnt that carrying an object and moving horizontally at a constant velocity has no work done. The truth is, there is a slight amount of work done due to overcoming air resistance in the horizontal direction.
Other than contributing to potential increase in diversity of species in an ecosystem, exotic species have positive benefits like removing toxins from the soil, regulating erosion, and controlling undesirable species.
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Cholera vaccination is only recommended for staff who have to intervene with patients in an epidemic situation. In all other cases, effective prevention is provided by good personal hygiene (washing hands) and food.
It is also important to know that this vaccine does not protect permanently: It protects only about 90% within 6 months, then to 50% within 3 years.
Capillaries have thin walls, only one cell thick, that allow them to effectively perform their function.
