If the isocost line is tangent to the isoquant line:

A: Marginal Product of labor/L is LESS than Marginal Product of capital/k

B: Marginal product of labor/L is GREATER than Marginal Product of capital/k

C: Marginal product of labor/L EQUALS Marginal Product of capital /K

D: Marginal Product of labor = Marginal product of capital

I don't think it is A OR B. (Can you also please explain this concept to me for better understanding?)