i.e. if you travel to Canada, and fly to China from Canada (even less than 30 days), you need turn in your I-94 when you leave US.
If somebody from the forum gives you something different, it is his/her own experience. The border office may not be strict. But you may get trouble some day if you do not turn in your I-94.
If you leave to China, please turn in your I-94. You will get a new one when you come back. I-94 is not a visa. Canadian does not need US visa; -- the TN or TD stamp on your passport is your "visa", or the approval letter (I-797) if you renew your status by mail in the US.
Hope my explanation would be clear.
If somebody from the forum gives you something different, it is his/her own experience. The border office may not be strict. But you may get trouble some day if you do not turn in your I-94.
If you leave to China, please turn in your I-94. You will get a new one when you come back. I-94 is not a visa. Canadian does not need US visa; -- the TN or TD stamp on your passport is your "visa", or the approval letter (I-797) if you renew your status by mail in the US.
Hope my explanation would be clear.