One Main Difference Between Maslow's Hierarchy and Alderfer's ERG Theory

One main difference between Maslow's hierarchy and Alderfer's ERG theory is that:

A) there is strong empirical support for Maslow's hierarchy but not for Alderfer's ERG theory.
B) Maslow's hierarchy of needs can operate simultaneously rather than sequentially as the ERG need categories do.
C) ERG need categories can operate simultaneously rather than sequentially as Maslow's hierarchy do.
D) Alderfer's work was mostly based on clinical observations, whereas Maslow conducted only empirical studies.