I131 form for Advance Parole

在填AP的申請表時有幾個問題：
1） class of admission -- what's this?
2) How many trips --- one or more than one? (if I select one, does it mean I can use it only once?)
3) Do I have to give the intended date of departure and the length of the trip? This does not have to be accurate, right?
請好心人幫助澄清一下，非常感謝！