Consider the following statements regarding relational database model:(a) NULL values can be used to opt a tuple out of enforcement of a foreign key.(b) Suppose that table T has only one candidate key. If Q is in 3NF, then it is also in BCNF.(c) The difference between the project operator (P) in relational algebra and the SELECT keyword in SQL is that if the resulting table/set has more than one occurrences of the same tuple, then P will return only one of them, while SQL SELECT will return all.One can determine that:

• A. (a) and (b) are true
• B. (a) and (c) are true
• C. (b) and (c) are true
• D. (a), (b) and (c) are true