题干
The teacher’s efforts ______ when one of his students was admitted to Beijing University last summer.
A：paid back
B：paid off
C：paid for
D：paid out
答案(点此获取答案解析）
B
两种方案的移动通。费用y(元)与通话时间x(元)之间的关系，则以下说法错误的是( )