Consumers are always willing to pay the most for the very first unit, and pay less for each additional unit. This idea is called: O the income effect
O the substitution effect
O diminishing marginal utility
O desire

The answer is diminishing marginal utility

Explanation:

Economists have identified a concept known as the law of diminishing marginal utility. It describes how the first unit of consumption of a good or service carries more utility than later units. ... Marginal utility is useful in explaining how consumers make choices to get the most benefit from their limited budgets

the option which was not a function of missionaries in the northwest was the first one - they established posts for trading furs and other goods.

missionaries were sent around the world to spread religion and their knowledge and others - they were not merchants who sold furs and other goods.