[单选题]Every morning,kids from a local high school are working hard．They are making and selling special coffee at a coffee cafe．They are also making a lot of money. These students can make up to twelve hundred dollars a day．They are selling their special coffee to airplane passengers．After the students get paid,the rest of the money goes to helping a local youth project. These high school students use a space in the Oakland airport．It is usually very crowded. Many people who fly on the planes like to drink the special coffee. One customer thinks that the coffee costs a lot but it is good and worth it．Most customers are pleasant but some are unhappy．They do not like it if the coffee care is not open for business. The students earn$6.10 an hour plus tips．They also get school credit while they learn how to run a business．Many of the students enjoy the work although it took some time to learn how to do it. They have to learn how to steam milk,load the pots,and add flavor．It takes some skill and sometimes mistakes are made．The most common mistake is forgetting to add the coffee． Most customers are pleasant but some are unhappy because__.
A.they don't think the skill to make coffee is necessary for students
B.they think the cafe should be open for business
C.they feel that the work is hard for students
D.they think the special coffee is too expensive