相关原文(the article related)：However, because there can be so many reactions in transfusions, patients usually receive only salt or plasma until their blood can be matched as exactly as possible in the blood bank of the hospital.
问题(question)：Usually, a person who has been injured and lost too much blood should be given a blood transfusion-----( )
A. after he receives salt or plasma
B. right after the accident happens
原因也写一下，谢谢！(Please tell me the reason, thank you!)
I think B is right, but my teacher said the correct answer is A. But I can't understand why.