问题
选择题
My persistence finally________when they called me in for an interview.[ ]
A. paid back
B. paid up
C. paid off
D. paid for
答案
答案：C
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My persistence finally________when they called me in for an interview.[ ]
A. paid back
B. paid up
C. paid off
D. paid for
答案：C
下列各组离子或分子能大量共存，当加入相应试剂后会发生化学变化，且发生反应的离子方程式书写正确的是
| 选项 | 离子组 | 加入试剂 | 离子方程式 |
| A | NH4+、Fe2＋、SO42- | 少量Ba(OH)2溶液 | 2NH4+＋SO42-＋2NH4+＋Ba2＋＋2OH－===BaSO4↓＋2NH3·H2O |
| B | Mg2＋、HCO3-、Cl－ | 过量NaOH溶液 | Mg2＋＋2HCO3-＋4OH－===2H2O＋Mg(OH)2↓＋2CO32- |
| C | K＋、NH3·H2O、CO32- | 通入少量CO2 | 2OH－＋CO2===CO32-＋H2O |
| D | Fe2＋、NO3-、HSO3- | NaHSO4溶液 | HSO3-＋H＋===SO2↑＋H2O |