The Cost Per Patient Day at Hospital a Is Much

The cost per patient day at Hospital A is much higher than the cost per patient day at Hospital B.This might be due to

A) Hospital A has sicker patients than Hospital B
B) Hospital A is an academic medical center and Hospital B is not
C) Hospital A has several long-term union labor contracts while Hospital B does not
D) Hospital B is more efficient than Hospital A
E) All of the above are possible