Final answer:
Rhizopus, a type of fungus, reproduces sexually through a process called heterogamy, which involves fusing hyphae from two different mating strains to form a zygospore.
Step-by-step explanation:
The fungus Rhizopus reproduces sexually through a process known as heterogamy. This process involves two different mating types, denoted as '+' and '-', which come together for sexual reproduction. During this process, the hyphae from the opposite mating strains meet and their gametangia fuse, leading to the fusion of haploid nuclei through karyogamy and the formation of a zygospore which is a thick-walled, resistant structure. Later, when environmental conditions improve, the zygospore germinates, undergoes meiosis, and releases haploid spores that grow into new organisms. This form of sexual reproduction, where two different mating types contribute to the formation of the offspring, is termed heterogamy (Option C).