Candidate keys

Question

Q18). Consider the table $R$ , with attributes $A,B,C,D$ and $E$. What is the largest number of candidate keys at the same time?

1. 1
2. 5
3. 10
4. 31

As we know number of candidate keys with n number of attributes  is $2^n -1$.Then how to solve this question?

Answer 1

10 is incorrect answer.

Comments

how? 10