The correct answer is: A. law of variable proportion.
The law of variable proportions states that as more and more of a variable input is added to a fixed input, the marginal product of the variable input will eventually decline. This is because as more and more of the variable input is added, the fixed input becomes less and less productive.
The law of increasing returns is a temporary phase of the law of variable proportions. This is because when a firm first starts to add more of a variable input, the marginal product of the variable input will increase. This is because the fixed input is still relatively productive and the variable input is being used in a more efficient way.
The law of constant returns is also a temporary phase of the law of variable proportions. This is because after a while, the marginal product of the variable input will start to decline. This is because the fixed input is becoming less and less productive and the variable input is being used in a less efficient way.
The law of diminishing utility states that as a consumer consumes more of a good, the marginal utility of the good will decrease. This is because the consumer will get less and less satisfaction from each additional unit of the good.
The law of proportionality states that if all inputs are increased by the same proportion, then output will also increase by the same proportion. This is because the inputs are being used in a more efficient way.
I hope this helps! Let me know if you have any other questions.