a person whose blood group is B required blood transfusion name the possible blood groups of the donors

if he is B negative :  he can only receive blood from other B negative donors or from type O negative donors

and if he is B positive : B positive patients can receive blood from B positive, B negative, O positive and O negative donors.  

Explanation:

it also supports my hypothesis. if you rest first you can squeeze the clothespin more times. from the data i collected the average of the eight people concluded exercise makes your muscles more fatigued and less able to squeeze the clothespin compared to resting before squeezing.