d
\(\mathrm{R}_{1}=\mathrm{R}_{0}\left(1+\alpha_{1} \mathrm{t}\right)+\mathrm{R}_{0}\left(1+\alpha_{2} \mathrm{t}\right)\)

\(=2 \mathrm{R}_{0}\left(1+\frac{\alpha_{1}+\alpha_{2}}{2} \mathrm{t}\right)\)

\(=\mathrm{R}_{0}^{\prime}\left(1+\frac{\alpha_{1}+\alpha_{2}}{2} \mathrm{t}\right)\)

Comparing with \(\mathrm{R}=\mathrm{R}_{0}(1+\alpha \mathrm{t})\)

\(\alpha=\frac{\alpha_{1}+\alpha_{2}}{2}\)