Final answer:
Based on the increase in sales for The Natural Pet and constant current accounts, the statement that must be true is 'The net working capital turnover rate increased' as it suggests higher sales efficiency without an increase in working capital.
Step-by-step explanation:
If The Natural Pet had sales of $763,500 in 2020, and $864,200 in 2021, and if the firm's current accounts remained constant, then we must identify which statement is true based on the given information. With an increase in sales and no change in current accounts, receivables turnover rate (net credit sales / average accounts receivable) would likely have increased if the accounts receivable remained the same. Thus, the option that the receivables turnover rate decreased (A) can be ruled out. Similarly, since the receivables turnover rate likely increased, the days' sales in receivables (365 / receivables turnover rate) must have decreased, not increased (B).
Without the amount of current liabilities or the net working capital provided, we cannot directly assess the net working capital turnover rate (C). However, the total asset turnover rate (sales / total assets) would have increased only if the total assets had remained constant or increased by a lesser percentage than the increase in sales, which is not given in the premise. Lastly, without specific information on fixed assets, we cannot assert whether the fixed asset turnover (sales / fixed assets) decreased (E). Based on the information provided, statement C, 'The net working capital turnover rate increased,' is most likely true as it suggests that since sales increased while current accounts (which are a part of net working capital) remained constant, indicating a higher efficient use of working capital.