Step 1: Stifling and brushing.
Freshly harvested cocoons are stifled (killed) and brushed to locate the filament end. Hence B comes first.
Step 2: Reeling.
The silk filament is unwound (reeled) from cocoons to form raw silk. Hence A comes second.
Step 3: Throwing.
The raw silk filaments are twisted together (throwing) to provide strength for weaving. Hence D follows.
Step 4: Degumming.
Finally, sericin (gum) is removed by boiling with soap solution, leaving lustrous silk. Hence C is last.
Step 5: Conclusion.
The correct sequence is B → A → D → C.