题目

阅读下面短文，从短文后各题所给的A、B、C和D四个选项中，选出可以填入空白处的最佳选项。The requirements for highschool graduation have just changed in my community. As a result, all studentsmust 1 sixty hours of service learning, 2 they will not receive a diploma. Servicelearning is academic learning that also helps the community. 3 of service learning include cleaning up apolluted river, working in a soup kitchen, or tutoring a student. 4 a service experience, students must keep ajournal and then write a 5 about what they have learned.Supporters claim that任何电路都是由电源、________、________和导线等组成的．干电池的锌筒是________极，碳棒是________极．