STM32 RTC ALLARM A and B selected problem

I use STM32F407 and program the internal RTC, date time work perfectly. But i have problem to set the alarm. Work only if set data in alarm A and alarm B, why not possible to set only alarm A ? or only alarm B ? This is my code for programming alarm, now set alarm when the seconds is the same the interrupt is generated in void HAL_RTC_AlarmAEventCallback(RTC_HandleTypeDef *hrtc), and after repeating the alarm every minute.. and so on.

sAlarm.AlarmTime.Hours = RTC_ByteToBcd2(n_Hour);
sAlarm.AlarmTime.Minutes = RTC_ByteToBcd2(n_Minute);
sAlarm.AlarmTime.Seconds = RTC_ByteToBcd2(n_Second);
sAlarm.AlarmTime.SubSeconds = 0x0;
sAlarm.AlarmTime.DayLightSaving = RTC_DAYLIGHTSAVING_NONE;
sAlarm.AlarmTime.StoreOperation = RTC_STOREOPERATION_RESET;
sAlarm.AlarmMask = RTC_ALARMMASK_DATEWEEKDAY|RTC_ALARMMASK_HOURS|RTC_ALARMMASK_MINUTES;//|RTC_ALARMMASK_SECONDS;
sAlarm.AlarmSubSecondMask = RTC_ALARMSUBSECONDMASK_ALL;
sAlarm.AlarmDateWeekDaySel = RTC_ALARMDATEWEEKDAYSEL_DATE;
sAlarm.AlarmDateWeekDay = RTC_ByteToBcd2(n_Day);
//
sAlarm.AlarmDateWeekDaySel = RTC_ALARMDATEWEEKDAYSEL_WEEKDAY;
sAlarm.AlarmDateWeekDay = BinToBCD(n_Day);
sAlarm.Alarm = RTC_ALARM_A;
if (HAL_RTC_SetAlarm_IT(&hrtc, &sAlarm, RTC_FORMAT_BCD) != HAL_OK)
{
    Error_Handler();
}
sAlarm.Alarm = RTC_ALARM_B;
if (HAL_RTC_SetAlarm_IT(&hrtc, &sAlarm, RTC_FORMAT_BCD) != HAL_OK)
{
    Error_Handler();
}

What did i forget for enabling only allarm A, for examples ?

thanks