Final answer:
The primary mode of HIV transmission in Sub-Saharan Africa is heterosexual sex (b). Secondary modes include transmission through contaminated blood and mother-to-child during pregnancy, childbirth, or breastfeeding.
Step-by-step explanation:
In Sub-Saharan Africa, the primary mode of transmitting HIV is through heterosexual sex. HIV, a sexually transmitted infection, is commonly transmitted through sexual contact, with the majority of global HIV transmissions resulting from heterosexual encounters. The pattern of HIV transmission does vary by region, though, with some areas experiencing different primary transmission routes.
Transmission through contaminated blood is the second most frequent mode, and this can happen via needle sharing, transfusion, or medical procedures with unsterilized equipment, particularly in nations where blood screening is less rigorous. However, due to the careful screening of blood and blood products, getting HIV from blood transfusions in wealthier nations has become virtually nonexistent.
Mother-to-child transmission is another significant mode of HIV spread, occurring during pregnancy, childbirth, or breastfeeding. Preventative measures and treatments can reduce the risk of vertical transmission significantly.