tHE INFO YOU NEED IS AT :
http://ada.org/prof/ed/testing/natboard/nbde_part01_candidate_guide.pdf
However if I understand you correctly , If you have an OVERALL passing grade WITH a PARTIAL PASS , In this , you are only allowed to take over the parts that you scored UNDER or LESS then 75. So if you scored over a 75 in THREE PARTS and UNDER a 75 in ONE PART you are only allowed to take the ONE in which you scored LESS then a 75 , in your case it is Bio/Physio . You have to retake this part with in 37 months from the date which you took the whole exam or you will recieve a COMPLETE FAILURE GRADE. Also you should know that you have only two chances at RE-taking this one failed part over . after a second attempt in retaking the one part , in the event you should fail both times you will recieve a COMPLETE FAILURE.
THAT IS HOW I UNDERSTAND THE INFO TO THE LINK ABOVE, CHECK IT OUT AND SEE .- BILL