根据公路滑坡防治设计规范》（JTG/T3334-2018）第5.4.9条，
$$\begin{array}{r l} \psi_ {6} & = \cos (\alpha_ {5} - \alpha_ {6}) - \sin (\alpha_ {5} - \alpha_ {6}) \tan \varphi_ {6} = \cos (2 6 ^ {\circ} - 2 0 ^ {\circ}) - \sin (2 6 ^ {\circ} - 2 0 ^ {\circ}) \tan 1 6 ^ {\circ} = 0. 9 6 5 \ & T _ {6} = F _ {s} W _ {6} \sin \alpha_ {6} - W _ {6} \cos \alpha_ {6} \tan \varphi_ {6} - c _ {6} L _ {6} + \psi_ {6} T _ {5} \ & = 1. 2 \times 2 6 3 5 \times \sin 2 0 ^ {\circ} - 2 6 3 5 \times \cos 2 0 ^ {\circ} \times \tan 1 6 ^ {\circ} - 1 9 \times 1 4. 1 + 0. 9 6 5 \times 2 7 8 0 = 2 7 8 6 k N \ \psi_ {7} & = \cos (\alpha_ {6} - \alpha_ {7}) - \sin (\alpha_ {6} - \alpha_ {7}) \tan \varphi_ {7} = \cos (2 0 ^ {\circ} - 1 5 ^ {\circ}) - \sin (2 0 ^ {\circ} - 1 5 ^ {\circ}) \tan 1 6 ^ {\circ} = 0. 9 7 1 \ & T _ {7} = F _ {s} W _ {7} \sin \alpha_ {7} - W _ {7} \cos \alpha_ {7} \tan \varphi_ {7} - c _ {7} L _ {7} + \psi_ {7} T _ {6} \ & = 1. 2 \times 2 4 7 2 \times \sin 1 5 ^ {\circ} - 2 4 7 2 \times \cos 1 5 ^ {\circ} \times \tan 1 6 ^ {\circ} - 1 9 \times 1 3. 4 9 + 0. 9 7 1 \times 2 7 8 6 = 2 5 3 2 k N \end{array}$$

参考答案：B