The correct answer is (d), Law of Constant Returns.
The law of diminishing returns states that in all productive processes, adding more of one input while holding all others constant will at some point cause the marginal (additional) output to decline.
The law of variable proportions is a more general statement of the law of diminishing returns. It states that as one input is increased while holding all others constant, the marginal product of that input will eventually decline.
The law of returns is a general term that refers to the relationship between inputs and outputs. It can be used to describe both the law of diminishing returns and the law of increasing returns.
The law of proportionality states that in the short run, the marginal product of an input is constant. This means that if you increase the amount of an input by a certain amount, the output will increase by the same amount.
I hope this helps!