题目

More and more public schools in America make it a rule that students must finish a certain amount of community service_61_they are allowed to graduate from high school.They work on projects like making the environment better or_62_(feed) homeless people. Many school systems in the United States now ask students_63_(do) some kinds of community service as part of their studies.Students involved in service projects help_64_(they) as well as their communities.They learn about the needs of people and aid_65_(organize).For this reason,holidays_66_(become) the prime period for volunteer work s长度的基本单位是： （ ）A. 千米 B. 米 C. 厘米 D. 纳米