The acceleration of the small slip ring sliding along the rod a = mgsinθ m = gsinθ,

According to rcos θ = 12at2, t = 2 rgsin θ cos θ = 4 rgsin θ, θ = 60 and 30 are equal, and θ = 45 is the shortest, so T 1 = T3 > T2. So d is correct, A, B, T2.

Therefore, choose: d.