Suppose that a firm in perfect competition is producing 6 tons of wheat with an average variable cost of $\textbackslash$50$/ton, an average total cost of $\textbackslash$70$/ton, and selling the wheat for a price of $\textbackslash$60$/ton. Will it make a positive or negative profit? Should this firm shut down? 
选项为:A:positive profit, don't shut down  B:positive profit, shut down  C:negative profit, don't shut down  D:negative profit, shut down  请回答其中一个选项.