Final answer:
The correct answer to the student's question is c) A relation can have more than one candidate key, as a relation may have multiple attribute combinations that uniquely identify tuples.
Step-by-step explanation:
The question pertains to the concepts of keys in the context of databases, which are an important part of database design and relational database management systems (RDBMS). In the context of this question, we can address the statements one by one:
- Superkey is a set of one or more attributes that, taken collectively, allow us to identify uniquely a tuple (row) in a relation (table). So, a) A superkey is indeed a type of key, but it may contain extra attributes that are not necessary for unique identification.
- b) By definition, if an attribute is a key, no two tuples can have the same value for that key. It is meant to uniquely identify each record.
- c) A relation can indeed have more than one candidate key, which are keys that satisfy the uniqueness property but are not necessarily chosen as the primary key.
Given these explanations, the correct answer to the question is: "c) A relation can have more than one candidate key." This statement is true because if there are multiple sets of attributes that can serve to uniquely identify each record in a table, each of them can be considered a candidate key.