Consider the following database table having $\text{A, B, C}$ and $\text{D}$ as its four attributes and four possible candidate keys $\text{(I, II, III and IV)}$ for this table :
$\begin{array}{|l|l|l|l|} \hline \text{A} & \text{B} & \text{C} & \text{D} \\ \hline \text{$a_1$} & \text{$b_1$} & \text{$c_1$} & \text{$d_1$} \\ \hline \text{$a_2$} & \text{$b_3$} & \text{$c_3$} & \text{$d_1$} \\ \hline \text{$a_1$} & \text{$b_2$} & \text{$c_1$} & \text{$d_2$} \\ \hline \end{array}$
$\begin{array}{} \text{I : {B}} & \text{II : {B, C}} & \text{III : {A, D}} & \text{IV : {C, D}} \end{array}$
If different symbols stand for different values in the table $(\text{e.g.,}\; d_1$ is definitely not equal to $d_2),$ then which of the above could not be the candidate key for the database table?
- $\text{I}$ and $\text{III}$ only
- $\text{III}$ and $\text{IV}$ only
- $\text{II}$ only
- $\text{I}$ only