The statement that best conveys how the author's viewpoint changes in the passage is:
3. His way of seeing the river shifts from mysterious wonder to objective analysis as he becomes a steamboating expert.
In the beginning, the author experiences a sense of wonder and beauty in the sunset over the river, appreciating its splendor. However, as he gains experience and becomes more knowledgeable about steamboating, his perspective shifts to a more analytical and practical approach, viewing the river's features in terms of safety and navigation rather than beauty.