sequential logic: d and j/k flip-flops
A D Flip-Flop is a component that operates off a clock, has outputs that are by definition inverses of each other and change on the clock pulse, has a reset and preset which set the component to a predetermined value when activated, and outputs the D input at each full clock pulse.
A J/K Flip-Flop is a universal flip-flop. If J and K are both inputed as logic 0's, then the output will be held. When J is a logic 0 and K is a logic 1, the flip flop is reset. When J is a logic 1 and K is a logic 0, the flip-flop is set. When both J and K are logic 1's, it works exactly the same as a D Flip-Flop. All other aspects of the flip-flop work like a D Flip-Flop.