题目内容：
Cost as a Factor in SupplyIn a purely competitive market,the supplier of goods and services has no control over.the market price,because he produces too little to influence market conditions.With no difference between his products and the products________ (1)his competitors,he will sell nothing if he charges above the market price and he will sell all if he charges at or________ (2)the market price.However, in considering the price,he must take the________ (3)of production into consideration.There are times when he may be willing to sell below his cost.This might happen when prices tumble for________ (4)he believes will be a short time.However, no business person can________ (5)to lose money for a prolonged period.He must be constantly________ (6)of his costs in relation to the market price if he is to compete successfully and earn a profit. Many people have the impression that as production increases。costs per unit decrease.________ (7)mass production has made this true in certain industries and at certain levels of production,________ (8)logic and practical experiences have shown that costs per unit begin to rise beyond a certain level of production.Some economists________(9)to this principle as the law of increasing costs.
The reason costs rise as production goes up is________ (10).However, it is easy to recognize that as production goes up.the need for additional factors of production will also grow,________ (1 1)competitive bidding in the marketplace for the factors of production.If a producer needs________ (12)skilled labor to produce more,and none of this labor is unemployed,the producer will have to get________ (1 3)from other sources.This can be done by________ (14)higher wages.Higher bidding would also apply to the other factors of production.We must also recognize that not all labor is equally productive,________ (15)not all land is equally fertile and not all ore(矿石)is equally rich in the mineral wanted.请选择（1）处的最佳答案 A．to
B．at
C．of
D．on
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