请问怎么理解good substitution

NO.PZ2016010801000045问题如下Monopolistic competition is characterizeby:A.substitutes: none, pricing power: some, barriers to entry: low, nature of competition: marketing.B.substitutes: goo pricing power: limite barriers to entry: high, nature of competition: aertisingC.substitutes: goo pricing power: limite barriers to entry: low, nature of competition: marketingC is correct.Goosubstitutes, limitepricing power, low barriers to entry anmarketing of procts are characteristiof monopolistic competition.考点垄断竞争市场解析垄断竞争市场上的商品是可以相互替代的。并且该市场的进入壁垒很低。厂商议价能力有限，因此要做市场推广营销。为什么是marketing 不是 aertising？

NO.PZ2016010801000045 substitutes: goo pricing power: limite barriers to entry: high, nature of competition: aertising substitutes: goo pricing power: limite barriers to entry: low, nature of competition: marketing C is correct. Goosubstitutes, limitepricing power, low barriers to entry anmarketing of procts are characteristiof monopolistic competition. 考点垄断竞争市场 解析垄断竞争市场上的商品是可以相互替代的。并且该市场的进入壁垒很低。厂商议价能力有限，因此要做市场推广营销。垄断竞争的商品都是差异化的，这个为什么选可替代呢，差异化应该是不可替代的吧

NO.PZ2016010801000045 pricepower讲义里写的不是some么，为啥A的some不对？

老师，monopoly competition中，冲刺的表单里写的是，firm是many的，gree of fferenof procts是some，进入壁垒是relatively easy，然后价格的控制是prisearcher，和现在这里的答案感觉不太一样呢。