What changes must be made to a 3-bit counter to make it a 4-bit counter answer?

By using JK flip-flops connected in the breadboard, we can able to create a 3-bit counter with sequences from 000 to 111. In order for us to create a 4-bit counter out from the 3-bit counter, we need to "Add another JK flip-flop where both J and K are 1".