What is the train value (G) in compound gear train?

• A. G = \(\frac{N6}{N1} = \frac{T1*T2*T3}{T2*T4*T6} \)
• B. G = N6 * N1 = T1+T2+T3+T4+T6
• C. G = N6 – N1 = T1 * T2 * T3 * T4 * T6
• D. G = \(\frac{N1}{N6} = \frac{T2*T4*T6}{T1*T2*T3} \)