An entrepreneur knits sweaters for sale. The entrepreneur has fixed costs of $100. When he makes 10 sweaters in one month, he must spend $15 on wool. To make eleven sweaters in one month, he must spend $17 on wool. If he has no other costs, what is the marginal cost of the eleventh sweater?

a) $1
b) $2
c) $17
d) $117

Ans: b) $2