A:NH4+、NO3﹣、CO32﹣、Na+
B:Na+、Ba2+、NO3﹣、HCO3﹣
C:SO42﹣、Fe3+、K+、Cl﹣
D:NO3﹣、K+、SO32﹣、Mg2+
_______ knowledge and experience are important to finish that task.
计算:(6xy2)(﹣2x2y)÷(﹣3y3)
按照要求作图: