How are spores produced sexually differ from spores produced asexually?

The common example of a zygomycete is black bread mold (Rhizopus stolonifera), a member of the Mucorales. It spreads over the surface of bread and other food sources, sending hyphae inward to absorb nutrients. In its asexual phase it develops bulbous black sporangia at the tips of upright hyphae, each containing hundreds of haploid spores. If the mycelia of complementary mating types are present, the fungus reproduces sexually and produces zygosporangia. Zygosporangia are typically thick-walled, highly resilient to environmental hardships, and are metabolically inert. When conditions improve, however, they germinate to produce a sporangium or vegetative hyphae. 

The answer would be d. pili