JNU 2011 pareto optimal alternatives

[vishnu]

Suppose there are 3 alternatives x,y and z; and 4 individuals 1,2,3 and 4.
Their ranking of the 3 alternatives are given below
R1:(xy)z
R2:yzx
R3:z(xy)
R4:(xy)z
 
Alternatives inside the brackets are indifferent to each other.If an alternative is written to the left of another alternative, then former is preffered to latter
Then set of pareto optimal alternatives is
a) {x.y}
b) {x.z}
c) {y,z}
d) none of the above.

The answer is c.
Can  any one explain  how the answer is reached?please help...
 

[divyas]

take for eg. allocation x
wen u move from x to y u'l see
R1 is indifferent
R2 is better off
R3 is indifferent
R4 is indifferent
so according to the definition of pareto efficieny v cn conclude that x is nt pareto efficient

and like this check for y to x , y to z
and from  z to x , z to y

u'l get the ans.