If a is average number of peaks more than 10 mm of uneveness per kilometre, b is average number peaks more than 6 mm for gauge variation per kilometre and c is average number of peaks more than 2 mm twist per metre, then composite current recording index (I c ), as recommended by Indian Northern Railways, is

• A. I c = 10 - a - b - c /4
• B. I c = 20 - a - b - c /4
• C. I c = 30 - a - b - c /4
• D. I c = 40 - a - b - c /4