21. Which number should a piano music lover dial for information？
22. What can you enjoy on a Sunday morning？
A. A recital.
B. An international book fair.
D. An exhibition of paintings.
C. A concert.
23. How is the last activity different from the other three？
A. It exhibits personal belongings.
B. It takes place in a different city.
C. It consists of 10 group members.
D. It is very attractive to music fans.
B Braving the freezing winter, group of Harvard students and teachers are training for April's Boston Marathon to raise money for the Philips Brooks House Association's（PBHA）Summer Urban Program as part of the Harvard College Marathon Challenge.
The Summer Urban Program is a network of ten summer academic camps for students aged five to nineteen from low-income backgrounds, and is managed by the PBHA. For more than a decade, the Harvard College Marathon Challenge, made up of students, teachers and former students, has raised thousands for charity（慈善） causes.