Option D is correct because profitability ratios are specifically calculated to analyse the earning capacity of the business. The context states that these ratios measure profits in relation to revenue from operations or funds (or assets) employed, which constitutes the 'return' on investment. In contrast, liquidity ratios measure the ability to satisfy short-term obligations, activity ratios measure the speed of converting accounts to revenue, and debt ratios measure the ability to service long-term debt.