4. In Chapter 9 , we studied the graph below. The curves represented in the (l,k) space are various isoquants of a given production function. The main takeaway of this graph is that: a. The production function displays increasing returns to scale. b. The rate of technical substitution (RTS) for a constant-returns-to-scale production function depends only on the k/ ratio and not on the level of production. c. The rate of technical substitution (RTS) for any production function depends only on the k/l ratio and not on the level of production d. The intersections between any ray through the origin and the various isoquants of a production function illustrate the problem of multicollinearity..