Option (A) Activity is correct. According to the textbook context, Activity (or Turnover) ratios 'indicate the speed at which, activities of the business are being performed.' These ratios 'express the number of times assets employed, or, for that matter, any constituent of assets, is turned into sales during an accounting period.' For example, Inventory Turnover Ratio 'determines the number of times inventory is converted into revenue from operations during the accounting period.' This directly matches the question's description about measuring the speed with which various accounts are converted into revenue from operations or cash. Other options like liquidity, debt (solvency), and profitability ratios serve different purposes - liquidity measures short-term paying capacity, solvency measures long-term debt servicing ability, and profitability ratios analyse earning capacity.