Which of the following stages in the life history of liver fluke infects the primary host?

The correct option is D Metacercariae

• Platyhelminthes contain worms that cause parasitic and non-parasitic infections in humans and other mammals. Liver fluke is an endoparasite.
• The fluke completes its life cycle with the help of two hosts. The primary host is sheep and its secondary or intermediary host is the freshwater snail.
• Liver fluke infects the snail at the miracidium stage and sheep at the metacercaria stage. Hence, option A is correct.