回複：請教8老師：我父母入境時沒I-94,填I-539怎磨辦？入境移民官隻蓋了個章和寫了有效居留期。

Get the I-94 at this website for the I-539 filing for the B2 extension:
https://i94.cbp.dhs.gov/I94/request.html;jsessionid=wS3zSDQWJ0bQRZNQhJRCbLLZRdP0592Ty05pqvTd1JS0KQvvhMfL!-1588311864