A relation (from the relational database model) consist of a set of tuples, which implies that
a) relational model supports multi-valued attributes whose values can be represented in sets.
b) for any two tuples, the value associated with all of their attributes may be the same.
c) for any two tuples the value associated with one or more of their attributes must differ.
d) all tuples in a particular relation may have different attributes.
