Examination of a relation rel_b reveals that no candidate keys exist. Given this information, it is necessary:?
a) re-examine the data, because someone made a mistake
b) use foreign key as a primary key
c) introduce a surrogate key to serve as a primary key
d) a and b
e) b and c
a) Is colA a primary key?
b) colE is a candidate key?
c) combination (colB, colC, colD) is candidate key