C. Islanders set up mock military posts and airstrips is the correct answer.
Cargo cults were religious movements that emerged in the southwest Pacific Islands during and after World War II. These movements were based on the belief that the Western goods and technology that arrived in the region during the war were gifts from the gods, and that by performing certain rituals and practices, the islanders could attract more of these goods and technology to their communities.
One result of the rise of cargo cults was that islanders began to set up mock military posts and airstrips, complete with bamboo control towers, wooden airplanes, and other improvised structures. These structures were intended to mimic the Western military and aviation technology that had arrived during the war, and to attract more of these goods to the islands.
The creation of these mock military posts and airstrips was a reflection of the islanders' desire to obtain the material wealth and technology that they believed had been bestowed upon the Western powers by the gods. However, this belief was ultimately based on a misunderstanding of the nature of the Western powers' military and economic might, and the islanders' attempts to copy these structures were largely ineffective in bringing about any significant change in their material conditions.