Many to One relation btw entity sets r1 and r2
I) assume r1 is left side of relation and r2 is right side of relation.
many entities of r1 connected to one entity of r2
A ----------> 1
B ----------> 1
C ----------> 1
D ----------> 2
E ----------> 3
by knowing the entity of r1, you can say what is entity of r2 ===> pk(r1) → pk(r2)
by knowing the entity of r2, you can not say what is entity of r1 ===> pk(r2) → pk(r1) is not hold
∴ pk(r1) → pk(r2) ===> Answer should be A
II) assume r2 is left side of relation and r1 is right side of relation.
many entities of r2 connected to one entity of r1
A ----------> 1
B ----------> 1
C ----------> 1
D ----------> 2
E ----------> 3
by knowing the entity of r2, you can say what is entity of r1 ===> pk(r2) → pk(r1)
by knowing the entity of r2, you can not say what is entity of r1 ===> pk(r1) → pk(r2) is not hold
∴ pk(r2) → pk(r1) ===> Answer should be B