At which stage in its life cycle does the silkworm yield the fiber of commercial use?

Here is a brief description of each option:

• A. Larva: The larva is the stage of the silkworm’s life cycle in which it feeds and grows. The larvae are called silkworms, and they spin silk cocoons around themselves as they pupate.
• B. Egg: The egg is the stage of the silkworm’s life cycle in which it begins its development. The eggs are laid by the adult moth, and they hatch into larvae.
• C. Pupa: The pupa is the stage of the silkworm’s life cycle in which it transforms into an adult moth. The larvae spin silk cocoons around themselves, and they pupate inside the cocoons.
• D. Imago: The imago is the stage of the silkworm’s life cycle in which it is an adult moth. The adult moths emerge from the cocoons, mate, and lay eggs.