Right answer is (c) Method of Independent Variables
The explanation is: Generally in order to know the seepage below the hydraulic structures the flownet is used. In other words we must solve the laplacian equations by mathematical method, or electrical method, or graphical method with the help of streamlines and equipotential lines and some boundary conditions. But, this is a time taking process and solving is more complicated. So, therefore for the designing of hydraulic structures khosla introduced a easy, simple and accurate approach called a method of independent variables.