find ck

Question

let x y z a b c be the attributes of an entity set.E.if {x},{x,y},{a,b},{a,b,c},{x,y,z} are superkeys then which of the following is candidate key?

a){x,y} and {a,b]

b){x} and {a,b }

c){x,y,z} and {a,b,c}

d){z} and {c}..with explanation

Answer 1

Option B

How ?

Candidate keys are a special subset of super keys that do not have any extraneous information in them.

Answer 2

candidate keys : if any proper subset of super key is also a super key then that Sk is not a candidate key,

so here .. x, xy , ab  , abc  ,xyz  .... these are Sk,  

for example 

x is proper subset of xy so, xy is not a candidate key BUT x is a Sk 

according to me Ckeys are   x,  ab  , 

SO OPTION B IS ANSWER