Concept:HIV/AIDS spreads mainly through unprotected sexual contact with an infected person, so prevention focuses on reducing risky sexual behaviour.
Explanation:HIV/AIDS can be transmitted through unprotected sexual intercourse, contact with infected blood, or from an infected mother to her child.
One of the most effective ways to prevent its spread is to avoid casual sexual activities.
Casual sex often involves multiple or unknown partners, which greatly increases the risk of exposure to the virus.
People should therefore be encouraged to abstain from casual sex or to remain faithful to one uninfected partner.
Marrying very early in life does not guarantee protection from HIV/AIDS.
Engaging in gainful employment or pursuing higher education also do not directly prevent the spread of the virus.
These options do not address the main route of transmission.
Answer:A. avoid casual sexual activities