Two heavy rotating masses are connected by shafts of lengths l1, l2 and l3, and the corresponding diameters are d1, d2 and d3, this system is reduced to a torsionally equivalent length of the shafts is

• A. \({{\rm{l}}_1} + {{\rm{l}}_2}{\left( {\frac{{{{\rm{d}}_1}}}{{{{\rm{d}}_2}}}} \right)^4} + {{\rm{l}}_3}{\left( {\frac{{{{\rm{d}}_1}}}{{{{\rm{d}}_3}}}} \right)^4}\)
• B. \({{\rm{l}}_1} + {{\rm{l}}_2}{\left( {\frac{{{{\rm{d}}_1}}}{{{{\rm{d}}_2}}}} \right)^3} + {{\rm{l}}_3}{\left( {\frac{{{{\rm{d}}_1}}}{{{{\rm{d}}_3}}}} \right)^3}\)
• C. \(\frac{{{{\rm{l}}_1} + {{\rm{l}}_2} + {{\rm{l}}_3}}}{3}\)
• D. l1 + l2 + l3