Answer:
b. Internal fertilization
Explanation:
Reproduction of molluscs is exclusively sexual. There are some hermaphrodite species, however, most are dioecious (separate sexes). Fertilization is usually internal, but may rarely be external. An example is the garden snail, which is monoecious. In copulation, two individuals of different sexes approach and touch their genital pores, fertilizing each other.
Development can be direct or indirect, the latter being the most common; The most well-known larval stages are the trochophor, similar to marine annelids.
