For problems 1-4, give all candidate keys for the tables with FDs specified.  Composite candidate keys must be put in parentheses, and candidate keys must be separated with commas or otherwise clearly specified.  For example, "A, B, C"  means that there are three candidate keys, but "(ABC)" means that there is one composite candidate key and "(ABC), E" means that there are two candidate keys, the composite of three colums (A B C) plus the single column E.  Please be very specific for full credit. 

1. What is (are) the candidate key(s) for a table with columns
                        A B C D E F G H I J
            and the following set of functional dependencies? 

A B → J

D → B

J→ C E F G H I

2. What is (are) the candidate key(s) for a table with columns
                        L M N O P Q
and the following set of functional dependencies? 

L→ M N

O → L P Q

3. What is (are) the candidate key(s) for a table with columns
                        A B C D E F G H I
  and the following set of functional dependencies? 

A → C D E F

E→G H I

6.What is (are) the candidate key(s) for a table with columns
                        M N O P Q R S T U
and the following set of functional dependencies? 

M →N O P

O P →M

N → Q R S T