Scenario 13-18 Farmer Jack Is a Watermelon Farmer. If Jack Plants No

Scenario 13-18
Farmer Jack is a watermelon farmer. If Jack plants no seeds on his farm, he gets no harvest. If he plants 1 bag of seeds, he gets 30 watermelons. If he plants 2 bags of seeds, he gets 50 watermelons. If he plants 3 bags of seeds he gets 60 watermelons. A bag of seeds costs $100, and the costs of seeds are his only costs.
-Refer to Scenario 13-18. What is the shape of Farmer Jack's marginal cost curve?

A) upward sloping
B) downward sloping
C) U-shaped
D) constant