Which conclusion is supported by the american public's shifting opinions about the panama canal over the course of the 20th century? a. people's points of view are unlikely to shift greatly unless their biases are first removed. b. historians cannot determine an event's true historical context until years after it is no longer relevant. c. even a period of only a few decades can greatly change the historical context surrounding an event. d. while people may change their political opinions, they rarely change their significant points of view.