1. To show that D=C^-1B^-1A^-1 in 2.2#17, we use
   a) associativity
   b) definition of multiplicative inverse to reduce to I
   c) definition of I as the multiplicative identity to remove it
   d) all of the above
   e) none of the above, because D is not C^-1B^-1A^-1.
   
   
   
   
2. Assume that A_nxn is invertible. Then the columns of A
   a) always span Rⁿ and I can explain why
   b) always span Rⁿ but I am unsure of why
   c) do not necessarily span Rⁿ but I am unsure of why
   d) do not necessarily span Rⁿ and I can explain why