Which of the following statements is true? a) minerals such as sodium chloride are priced lower because they are necessary for life, while decorative metals such as gold for jewelry making are priced higher because they are luxuries. b) the trend is moving away from using surface mines, because they cause so much collateral air and water pollution. c) a mineral deposit may become reclassified as a mineral reserve if the price of the element or compound rises due to scarcity. d) environmental regulation lowers the cost of mining.