Statement T or F 1 Any key is a super key but not any super key is a key 2 We can have more than one candidate keys in a table 3 A column that is referenced by a foreign key must be a candidate key 4 A foreign key cannot be NULL 5 All candidate keys are superkeys 6A primary key value cannot be null. 7 Duplicate rows are allowed in a table but not in a relation 8A proper subset of the columns in a super key cannot be a super key