Android Alarm What is the difference between four types of Alarm that AlarmManager provides and when to use what?

I want to know the difference between RTC, RTC_WAKEUP, ELAPSED_REALTIME, ELAPSED_REALTIME_WAKEUP.
I want to write an alarm application where I will set alarm and close my application and expect for alarm for the time set.
There will be multiple alarms. Right now I am writing for emulator but later will test on device. In emulator, once I set the alarm and close the emulator and restart it, then will it be cleared, as I find with RTC, RTC_WAKEUP and ELAPSED_REALTIME. I am confused. Should I used ELAPSED_REALTIME_WAKEUP? I have not seen any tutorial using ELAPSED_REALTIME_WAKEUP. please explain. Thanks.