In the $1820$ ?s $,$ ?a Hudson's Bay Company employee was dispatched to implement this strategy to dissuade Americans from settling in the Columbia River valley:

a $.$ ?deliberately depleting beaver populations in one of the Columbia's major tributary rivers

b $.$ ?initiating a steamboat line in the upper Columbia, thus undermining American competitors

c $.$ ?forging an alliance with the Cayuse to resist American encroachment in the region

d $.$ ?installing boundary markers along the Rocky Mountain divide, asserting HBC $\text{'}$ s claim to all lands westward