Explanation:
In this question, we need to determine which flip-flop has a clearly defined output for all combinations of two inputs. Let's analyze each type of flip-flop one by one:

a) R-S Flip-Flop:
The R-S (Reset-Set) flip-flop is an asynchronous flip-flop that has two inputs: R (Reset) and S (Set). It can have four possible combinations of inputs: 00, 01, 10, and 11. However, when both inputs are set to 1 (11), it results in an indeterminate state known as a "race condition". In this state, the output can oscillate between 0 and 1 rapidly, making it unclear and undefined. Therefore, the output of an R-S flip-flop is not clearly defined for all combinations of two inputs.

b) J-K Flip-Flop:
The J-K flip-flop is an asynchronous flip-flop that has two inputs: J (Jack) and K (King). It can also have four possible combinations of inputs: 00, 01, 10, and 11. However, the J-K flip-flop has an additional feature compared to the R-S flip-flop. When both inputs are set to 1 (11), instead of entering an indeterminate state, the output toggles or changes its state. This toggle operation makes the J-K flip-flop useful for various applications, such as counters and frequency dividers. The output of a J-K flip-flop is clearly defined for all combinations of two inputs.

c) D Flip-Flop:
The D flip-flop is a synchronous flip-flop that has a single input: D (Data). It can have only two possible combinations of inputs: 0 and 1. The output of a D flip-flop depends only on the present state of the input. It does not have any indeterminate or undefined states. Therefore, the output of a D flip-flop is clearly defined for all combinations of two inputs.

d) None of these:
The correct answer is not "None of these." As explained above, the J-K flip-flop is the only flip-flop among the given options that has a clearly defined output for all combinations of two inputs.