請問一個彈性的問題 - 經濟

A perfectly inelastic supply curve in a competitive market:

a. Means the equilibrium price must be zero.
b. Implies a vertical demand curve.
c. Exists when firms cannot vary input usage.
d. Says the market supply curve is horizontal.


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答案是c，我只知道perfectly inelastic supply curve是vertical的，
也就是產品價格的改變並不能去影響廠商供給的量，
請問一下這要怎麼推論到c答案的那個結論阿，謝謝!!


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記得我曾對妳說....
對妳說....
妳不知道我的哀愁是怎樣一回事


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