Concept:Ratio compares two quantities only if they are in the same unit.Explanation:First, convert 10 m into centimetres. Since 1 m = 100 cm, multiply: 10 × 100 = 1000 cm.Now both values are in cm: 1000 cm and 50 cm.Write the ratio as 1000 : 50.Simplify by dividing both numbers by 50. 1000 ÷ 50 = 20, and 50 ÷ 50 = 1.Thus the simplified ratio is 20 : 1.Answer:B. 20:1