回複：Then I have two I-797B, both without I-94

which one I should use to apply for visa?

-Depends on which employer you want to work for after you return to US. This is your choice. But if the second employer is the industry company, you can not work for them until Oct. 1 if you have never worked for the industry company before and that means you can not enter US until September 21 in this case. 

I got one I-797B on 04/15/2011, the other will be issued within 10 days.