Questions

Answer D is correct because a sunk cost is a project expense that will eventualy need to be paid. Answer A is incorrect because a fixed cost remains constant, regardless of any change in a company's activity. Answer B is incorrect because direct cost can be directly linked to producing specific goods or services. Answer C is incorrect because a variable cost changes in proportion to a change in the company's activity or business.

It will stop at a height where the weight of the balloon with contents is equal to the weight of air displaced by it, i.e , when the upthrust is equal to the downthrust. The question of bursting will depend on how much difference of pressure inside and outside , the material of the balloon can withstand. It is assumed the balloon is filled with a lighter than air gas like hydrogen or helium.

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Hydroelectricity is electricity produced from hydropower i.e, water.

Passivity of iron is due to formation of an extremely thin and impervious film of ferrosoferric oxide Fe3O4on the surface of iron. Chromic acid, being a powerful oxidising agent (like nitric acid ) renders iron passive. 

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