Answer:
C. Sharing a dinner utensil
Step-by-step explanation:
STIs stands for Sexually Transmitted Infections, which are infections due to bacteria, viruses or parasites transmitted while intercourse or contact with that zone genital to genital.
Among the options, sharing a dinner utensil doesn't represents a risk of getting an STIs, because genitals are not involved basically.
Therefore, the right answer is C.