A closed thin-walled tube has thickness, $t$, mean enclosed area within the boundary of the centerline of tube’s thickness, $A_m$, and shear stress, $\tau$. Torsional moment of resistance, $T$, of the section would be

- $0.5 \tau A_m t$
- $\tau A_m t$
- $2 \tau A_m t$
- $4 \tau A_m t$