In Du Fu's "Ascending the Mountain", which sentence is an expression of concern for the country and the people? Please analyze this sentence briefly.

"I came from three thousand miles away. Sadness follows the autumn today, and I am sad for a hundred years, and I climb this high alone "further clarifies the feelings contained in the above two couplets, and shows the melancholy of the poet when he is worried about the country and hurts the country in time and space: one is sad and wandering, and Wan Li leaves his hometown; Two sad late autumn bleak, desolate and magnificent; Life is short and moody; Four sorrows travel to other places and visit other places; Five sad old people climb mountains, unable to do so; Six sorrows are weak and sick, and the situation is difficult; Seven worries about loneliness are hard to send ... The neat and rigorous confrontation is full of the poet's endless travel worries like fallen leaves, and the poet's endless loneliness and hatred like a river, which makes us deeply feel the pulse of Du Fu's heavy beating feelings and the strong voice of the times!