Answer: Being sexually active, especially with more than one partner.
Step-by-step explanation:
STI stands for sexually transmitted infection. It infects the genital part of an organism during sexual intercourse and other ways.
These are the following reasons for STI:-
Sexual intercourse without using condoms.
sexually active with more than one partner.
Blood transfusion with the infected persons.
In some cases, The intravenous drug is also responsible for the STI due to sharing the same needle, which results in transfusion of blood with the infected person.