Consider the relation $T(A1,A2,A3,A4,A5,A6,A7)$ and the following functional

dependencies:

$A1A3$

$A2A4$

$A4A5$

$\{A1,A2\}\{A6,A7\}$

$A6A1$

$A7A2$

Which of the following statements is TRUE?

$($A$)($A$1,$ A$3)$ is a key.

$($B$)(A3,A6,A7)$ is a key.

$($C$)(Al,A4,A7)$ is a key.

$($D$)(A2,A6)$ is a key.

$($E$)(A1,A2)$ is a key.