Isinglass is used principally as:

Correct option is A

Isinglass is a collagen product obtained from fish swim bladders (sturgeon, etc.) used as a fining agent to remove suspended solids and clarify beverages.
Composition: collagen proteins that carry a positive charge in solution.
Action: binds negatively charged suspended particles (yeast, haze) → aggregates → sedimentation.
Method: small doses are added post-fermentation; after settling, clarified liquid is siphoned off.
Uses / Applications
Widely used in traditional winemaking and brewing for bright, clear appearance.
Also historically used in some adhesives and glues but principal industrial use is fining.
Notes on other options
Manufacture of stamps, making pearls: not principal uses.
Some breweries avoid it for vegan labeling.