题干
Volunteering our time to help people ________ a good way to _______our free time.
A：be; spend
B：are; cost
C：is; spend
D：will; cost
答案(点此获取答案解析）
C
Volunteering our time to help people ________ a good way to _______our free time.
A：be; spend
B：are; cost
C：is; spend
D：will; cost
是同类二次根式的是（ ）.
