Handle$:$
A Handle is a Substring that matches the body of production and whose reduction represents one step along the reverse of the right most derivation.
If we say more precisely $:$
$* \ Source: Ullman$
Now the given Right most derivation :
$ S1$ $\Rightarrow$ $Sc$ $\Rightarrow$ $SAC$ $\Rightarrow$ $SaSbc$
Here in the right-sentential form, replacing $aSb$ by $A$ produces the previous right-sentential form.
So the handle is $A → aSb$
Correct Ans : Option D