Given the following data for the tasks in a production process, which of the following tasks have non$-$zero slack times?

Task name

Duration $($days$)$

Immediate Predecessor

A

$5$

$-$

B

$2$

A

C

$3$

A$,$ B

D

$3$

A

E

$4$

D

F

$2$

C$,$ E

F

E

D

C