Suppose There Are 11 Buyers and 11 Sellers,each Willing to Buy

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.If there is a market maker in this market.What is the profit maximizing bid-ask spread per unit for a market maker?

A) ​$6 bid;$12 ask
B) $7 bid;$11 ask
C) $8 bid;$10 ask
D) ​$9 bid;$9 ask