Durant is a leading manufacturer of armored vehicles for the U.S. Armed Forces. Durant has been able to secure many contracts because of its use of duranium, a rare metal that is difficult to locate and extract. Currently only one company, Minekraft, mines and supplies duranium. According to Porter's Five-Forces model for industry analysis, which force should Durant be most concerned with regarding Minekraft? a. Threat of substitute products and services b. Threat of low resource allocation c. Rivalry among competitors d. Bargaining power of buyers e. Threat of new entrants f. Bargaining power of suppliers