我们在网上看了一下,好想需要A photocopy of confirmed onward air ticket or flight itinerary. A valid visa to the next destination should be obtained (if applicable). If you are returning to USA after visiting Singapore, please produce a valid US visa or relevant documentary proof confirming your returnability, eg. INS Parole Paper, etc. 那是要在办签证以前就要买机票吗?好像不太合理。