Correct option is A
Coherence and Flow:
Introduction (B) provides the initial context about the Braille stamp.
Design Details (D) describes the specific features of the stamp.
Historical Context (C) gives additional information on the first raised-dot Braille stamp.
Conclusion (A) ties the paragraph to a significant event in the history of Braille stamps.
Thus, the sequence BDCA creates a logical and coherent flow, making option (a) the correct answer.