Which era came immediately after World War II?

Leading guitar string producer wound up inc. has enjoyed a competitive advantage based on its proprietary coating that gives its strings a clearer sound and longer lifespan than uncoated strings. one of wound up's competitors, however, has recently developed a similar coating using less expensive ingredients, which allows it to charge a lower price than wound up for similar-quality strings. wound up's competitive advantage is in danger due to a. a lack of perceived value b. a lack of organization c. direct imitation and substitution d. resource immobility