Given table r(a, b,c) and s(c, d,e), which of the following sql statements would find the record(s) with null values on the column c in table s?
a. select * from r, s where r. c = s. c (+); (r left outer join s)
b. select * from r, s where s. c = r. c (+); (r right outer join s)
c. either a. or b.
d. neither a. nor b.

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