Answer:
b. the marginal cost of one more glass of lemonade is smaller than if output were high.
Step-by-step explanation:
Since the Thirsty Thelma operates in small lemonade stand and when she produced a low quantity of lemonade she has fewer workers plus her equipment is also not fully utilized
So she put her idle resources to use for one more glass of lemonade as if its output is high
Hence, the second option is correct