Compared to Having Unprotected Heterosexual Vaginal Intercourse, Receiving Oral Sex

Compared to having unprotected heterosexual vaginal intercourse, receiving oral sex is:

A) more likely to transmit HIV, but less likely to spread other STIs.
B) very unlikely to transmit HIV or any other STI.
C) a low risk for transmitting HIV, but still a potential risk for other STIs.
D) equally likely to transmit HIV as well as other STIs.