let a , b , and c be, respectively, 3 × 2, 2 × 3, and 3 × 3 matrices. then a ( bc ), b ( ca ), and b ( ac ) are all defined.
a) All three are defined.
b) Only A⋅(BC) is defined.
c) Only B⋅(CA) is defined.
d) Only B⋅(AC) is defined.
e) None of them are defined.