Final answer:
Revenue per customer, accounts receivable, and inventory turnover are external metrics for a company.
Step-by-step explanation:
An external metric for a company refers to a measure that assesses the company's performance from an external perspective, taking into account factors that are not directly controlled by the company. Among the options given, revenue per customer, accounts receivable, and inventory turnover are external metrics.
Revenue per customer measures the average amount of money generated by each customer, which is influenced by factors such as pricing strategies and customer loyalty programs. Accounts receivable represents the amount of money owed to the company by its customers, which reflects the effectiveness of the company's credit and collection policies. Inventory turnover measures how quickly a company is able to sell its inventory, indicating its efficiency in managing stock levels and meeting customer demand.