【单选题】
A <{p}><{font _mstmutation="1" _msthash="20524" _msttexthash="28885233"}>随产量增加而减少<{/font}><{br/}><{/p}>
B <{p}><{font _mstmutation="1" _msthash="20525" _msttexthash="28739906"}>随产量增加而增加<{/font}><{br/}><{/p}>
C <{p}><{font _mstmutation="1" _msthash="20526" _msttexthash="46611253"}>在各种产量水平下保持不变<{/font}><{br/}><{/p}>
D <{p}><{font _mstmutation="1" _msthash="20527" _msttexthash="46740356"}>在不同产量水平下各不相同<{/font}><{br/}><{/p}>
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