Which of the following is correct?

a. A distinct data type is a user-defined data type which specializes a standard, built-in SQL data type.

b. An opaque data type is an entirely new, user-defined data type, which is not based upon any existing SQL data type.

c. An unnamed row type allows inclusion of a composite data type in a table by using the keyword ROW.

d. A named row type is a user-defined data type that groups a coherent set of data types into a new composite data type and assigns a meaningful name to it.

e. All of the above are correct.