Final answer:
B. Conservationist
The events of John Muir founding the Sierra Club and the establishment of the National Parks Service were part of the Conservationist movement, which aimed to preserve natural environments and promote sustainable resource management.
Step-by-step explanation:
The events mentioned, the founding of the Sierra Club by John Muir and the establishment of the National Parks Service, are part of the Conservationist movement. This movement began in the 19th century and gained significant momentum in the United States at the start of the 20th century, primarily due to the efforts of figures like John Muir. The Conservationist movement aimed at preserving natural areas and wildlife, as well as promoting the sustainable management of natural resources. John Muir, in particular, was known for his belief in the inherent value of nature, beyond its utilitarian value to humans, which became a pivotal part of environmental protection and preservation policy in the US.