加工一批零件，甲单独做6小时完成，乙单独做9小时完成，甲、乙合做______小时

Kuss Middle School serves students in Fall River, Mass. , a former mill town that has struggled economically for decades. Students at Kuss have struggled, too, usually falling short of making the academic progress required under the No Child Left Behind law.
Then, last year, the school experimented with extending the school day. Teachers got paid at a higher hourly rate.
Students weren't thrilled at first with leaving school at 4:15 p.m. instead of at 2:20 p.m. But the added hours gave them more time for physical education and let them select special interest classes. By the end of the year, student scores had risen by enough to enable Kuss to make the progress required under the federal No Child Left Behind law.
The only surprise is that more districts haven't lengthened school schedules set decades ago to accommodate (适应) a farm economy rather the information economy of today.

School days The USA ranks 36th of 40 industrialized nations in average weekly instructional time. Selected countries: 1) Thailand--30.5 hours  2) Korea--30.3 hours  7) China--26.5 hours 14) France--24.6 hours  15 ) UK--24.6 hours 16) Mexico--24.2 hours  23 ) Japan--23.8 hours 26)Canada--23.6 hours  36)USA--22.2 hours  40)Brazil--19 hours

New research suggests the time is ready for a change:
Matched against 39 other developed countries, the United States is near the bottom in the rankings of average weekly instructional time in school.  Measured over 12 years, students in the top-scoring countries spend the equivalent of a full extra year in school.
US students perform poorly on math and science tests compared to their international peers, according to a US Education Department comparison released earlier this month. In math, American 15-year-old scored near the bottom among the study's 30 developed countries.
Most countries that boost the number of minutes spent on math instruction find pay offs in improved math scores, according to a study released this month by the Brookings Institution. Small in creases in the school day are more effective than a longer school year, the report concluded.
The most encouraging news about the benefits of extending the school day comes from Massachusetts, where an experiment with 10 schools, including Kuss, appears to be working. Those 10 schools lengthened their instructional days by 25% and boosted their state scores in math, English and science at all grades.
Perhaps the concept won't work everywhere. Certainly, it won't instantly be popular. But it's obvious that a problem exists or that adding class time seems to help.
小题1:What is the main idea of the above passage?

A．Experiments with extended school hours produce academic gains.

B．Kuss Middle School sets a good example for US education.

C．Academic progress has achieved under the No Child Left Behind law.

D．Information age calls for more instructional lime at all schools.

小题2:A longer school day is suggested for the following reasons except that _________.

A．students from many developed countries spend more time at school

B．American students do a bad job at science subjects

C．teachers are paid at a higher rate with time added

D．a longer school day works better than a longer school year

小题3:Which statement is true of Kuss Middle School?

A．Kuss Middle School lies in where a farm economy is changing to an information one.

B．Kuss Middle school has joined the federal "No Child Left Behind" progrann

C．Neither teachers nor students are happy with the longer school day.

D．Adding class time functions at Kuss Middle School.

小题4:The writer has expressed ____________.

A．a positive attitude towards adding school time

B．a negative attitude towards adding school time

C．a changing attitude towards adding school time

D．a right attitude towards adding school time