To make an eight$-$bit adder from two four$-$bit adders you must connect

Question $4$ options:

A$)$

the high$-$order carry$-$in to ground.

B$)$

the low$-$order carry$-$out to high$-$order carry$-$in$.$

C$)$

the high$-$order carry$-$out to ground.

D$)$

the low$-$order sum to the high$-$order data input.