Activities of three radioactive substances $\mathrm{A}, \mathrm{B}$ and C are represented by the curves $\mathrm{A}, \mathrm{B}$ and C , in the figure. Then their half-lives $T_{\frac{1}{2}}(A): T_{\frac{1}{2}}(B): T_{\frac{1}{2}}(C)$ are in the ratio
