The L-shaped isoquant implies that production requires that the input

The correct answer is: B. Must be used together in a certain proportion.

An isoquant is a curve

that shows all the combinations of inputs that can be used to produce a given level of output. An L-shaped isoquant implies that the two inputs must be used together in a certain proportion. This is because the two inputs are complementary, meaning that they are used together to produce the output. If one input is increased, the other input must also be increased in order to maintain the same level of output.

Option A is incorrect because the two inputs can be used together. Option C is incorrect because the two inputs are complementary, not imperfect substitutes. Option D is incorrect because the two inputs are not perfect substitutes.