单选题：Questions are based on the following passage. 　　Some people

Questions are based on the following passage.
　　Some people say the traditional calendar of 180 days no longer meets the needs of American society. They point out that students in most other industrial countries are in school more hours a day and more days a year. Critics also say a long summer vacation causes students to forget much of what they learned and schools are under pressure to raise test scores. Some schools have changed their calendars to try to improve student performance. They have lengthened the school day or added days to the year or both. This can be costly if schools need air conditioning on hot days and school employees need to be paid for the extra time.
　　Some schools have a year-round schedule. The school year is extended over twelve months. Instead of a long vacation, there are many short ones. Local businesses may object to a longer school year because students are unable to work as long at summer jobs. Some parts of the country had year- round programs in the nineteenth century, mostly for economic reasons. They felt it wasted money to use school buildings for only part of the year. Year-round programs can also reduce crowding in schools. In one version, students attend school for nine weeks and then have three weeks off. The students are in groups that are not all in school at the same time.
　　Another year-round calendar has all students in school together for nine weeks and off for three. This is meant to provide the continuous learning that can be lost over a long break. But year-round schooling has opponents. They say it can cause problems for families when they want to make summer plans. And they say it interferes with activities outside school -- including summer employment.
　　Some experts say no really good studies have been done to measure the effect of school calendars on performance. But some educators think year-round schooling especially helps students from poor families that lack educational support at home.

The best title for the passage seems to be A．Debating upon Year-round Schooling
B．Advantages of Year-round Education
C．Disadvantages of a Long Summer Vacation
D．Different Types of School Calendars