Can someone please tell me why C) IS NOT the RIGHT ANSWER?

I know the answer is b) and fully understand why b) is right, but I would like to know the exact reason why C) is incorrect.

10. For production to take place in the rm, the workers must supply some effort. Suppose that with the status quo best response curve in the gure below, the firm chooses the wage to minimize the cost of effort, and the worker's best response is an effort level of 0.6. 1 1 Status we best response tuwe 0 u: 3 .8 I. It '5 E O o $35.31: w Hourly wage. w (5) Which of the following statement must be true in equilibrium? a) If the disutility of effort rises, then effort will fall. b) Ifunemployment rises, then the wage will fall c) Any combination of e and w that is both on the isocost line and the best response curve is a Nash equilibrium