Explanation:

- The story begins with the narrator's observation. So, the sentence "B. I was going to the market when I saw a blind man trying to cross the street." should be first.

- Following this, "D. I walked across to the blind man." is the logical next step, as the narrator approaches the blind man.

- After reaching the blind man, it's likely he would assist him, thus "A. Then I took him by the hand and led him across the street." comes next.

- Lastly, expressing gratitude makes sense after receiving help, so "C. He expressed his gratitude with folded hands." concludes the paragraph.

- Therefore:

- BDAC forms a coherent sequence.