a
Torque created due to weight of street light remains same in all the three cases. It is balanced by torque created by tension in the string. So if \(t\) be the torque created by weight of lamp and \(T\) be tension in the string and \(d\) be perpendicular distance of cable from the axis then
\(\tau = T.d\)
Tension will be least for largest \(d\). This is in pattern \(A\). So Pattern \(A\) is more sturdy