Read the following context and choose the best option to answer the question.
Context: I recently flew UA to S. America , scrounging UA miles to upgrade to Business Class . After making the reservation , I put my US DM # into the reservation for credit ( I need credit to make Elite level ) . But when I got to the airport , UA had removed the US number and re - inserted the UA number , so I changed it and asked them to change it for the whole itinerary .
Question: Why did he enter the US number ?
Options: 
A. So he could get better airline status .
B. He wanted to upgrade to business class .
C. None of the above choices .
D. The UA DM number would get his extra status .


A