The correct answer is C. Zero.
Marginal utility is the additional satisfaction or benefit that a consumer gains from consuming one more unit of a good or service. At a point of satiety, the consumer has consumed so much of the good or service that they no longer derive any additional satisfaction from consuming more. In other words, the marginal utility of the good or service is zero.
Option A is incorrect because marginal utility cannot be negative. This is because consumers will always choose to consume goods and services that provide them with positive utility.
Option B is incorrect because marginal utility can be positive at points before satiety. This is because consumers will always choose to consume more of a good or service as long as the marginal utility is positive.
Option D is incorrect because marginal utility cannot be highly positive at points of satiety. This is because the marginal utility of a good or service will always decline as the consumer consumes more of it.