If all factors are required to be used in fixed proportions, then the Law of Variable Proportions -
Law of Variable Proportions is the law to examine the production function with one factor changeable, keeping the quantities of other factors fixed. In other words, it refers to the input-output relation when output is increased by changing the quantity of one input.
Better utilization of the fixed factor the supply of the fixed factor is too large, where variable factors are too few. It results in increased effectiveness of variable factor and indivisibility of unchanging factor.
Thus, the correct option is B.