Explanation: Determining the condition of a battery accurately requires more than just checking its open-circuit voltage. **Option A (Measuring voltage under normal load)** is crucial. As a dry cell "B" battery (a primary cell, typically carbon-zinc) discharges, its internal resistance increases. When you measure the voltage *under load*, this increased internal resistance causes a greater voltage drop across the battery terminals compared to a new battery. A battery that shows good voltage with no load might collapse significantly under even a small current draw if it's nearing the end of its life. **Option C (A loss of 20% of the voltage under normal load indicates that the battery should be replaced)** provides a practical guideline. A 20% drop from the nominal voltage under normal operating conditions signifies significant degradation in the battery's ability to supply power and maintain voltage, indicating it's time for replacement to ensure reliable operation. **Option B (Measuring voltage under no load)** is generally unreliable for determining a battery's true condition because it doesn't reveal the internal resistance or its ability to deliver current. Therefore, combining the practical method of load testing with a common replacement threshold makes **D (A & C)** the most complete and correct answer.