Here the answer is option :C.
Case 1: for S1 there it is said that b is Linear combination of column of A so there will be solution
now weather the solution is unique or whether it is infinite it depends on Columns of A are linear independent or linearly dependent
IF the columns are L.I then there is a unique solution and if they are L.D there is infinite solution
so S1 is true
CASE 2 : for S2 it is said that b is linear dependent on Columns of A and there is a unique solution whic is false because if b is L.D then there is always infinite solution