US visa valid period?

I am H1B staying in Texas. Plan to attend a trade show in Italy in October. My questions are: 1. should I apply US re-entry visa in Mexico? 2. How long is the valid period for the visa? 3. Is it a multi re-entry visa? 4. If it is 2 entry visa, will it consume '1 entry' when I apply in Mexico and come back?
Waiting online. Thanks a lot.

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• 回复：US visa valid period? -sleepingtiger- ♂ (63 bytes) () 03/16/2007 postreply 02:51:34