Subjective probabilities are derived mathematically from reliable historical data.

​Suppose there are 11 buyers and 11 sellers,each willing to buy or sell one unit of a good,with values {$14,$13,$12,$11,$10,$9,$8,$7,$6,$5,$4,}.Assume no transaction costs and a competitive market.At the optimal bid,ask spread,what is the total profit that the market maker makes?

A) ​$8
B) $12
C) $18
D) ​$20

A net increase in inventories is considered as investment for the current year.