题干
David didn't attend his daughter's graduation ceremony, but he does wish he there.
A：should be
B：would be
C：had been
D：were
答案(点此获取答案解析）
C
，其中K-介予和
介子是带负电的基元电荷，
介子不带电。一个K—介子沿垂直于磁场的方向射入匀强磁场中，其轨迹为圆弧AP，衰变后产生的
之比为2:1。如图所示，