Adolescents ages 15-24 account for nearly half of the 20 million new cases of STD's each year. Today, two in five sexually active teen girls have had an STD that can cause infertility and even death. Also, though rates of HIV are very low among adolescents, males make up more than 80 percent of HIV diagnoses among 13- to 19-year-olds. STDs often have no obvious sign or physical symptom, so regular screenings are critical. The most effective way to prevent STDs is to abstain from sexual activity; if teens are having sex, they should be using a condom correctly and with every sexual act.

– “Sexually Transmitted Diseases,”
Office of Adolescent Health, CDC

Which statement best explains the long-term consequence a young woman may experience as a result of sexual activity as a teen?

Young women will not experience long-term consequences of sexual activity if they use condoms.
Young women are more likely to contract HIV between the ages of 13 and 19.
Young women may not be able to find a partner free of STDs later in life.
Young women may not be able to conceive children as a result of contracting an STD as a teen.

The statement that best explains the long-term consequences a young woman may experience as a result of adolescent sexual activity is that young women may not be able to conceive children as a result of contracting an STD as a teen (last option).

Explanation:

The report clearly explains that "Today, two in five sexually active teen girls have had an STD that can cause infertility and even death.", so infertility is a possible effect of unprotected sexual practices in teen girls.

Diseases such as gonorrhea and chlamydial infection can lead to pelvic inflammatory disease that, in the long term, can lead to blocked fallopian tubes and secondary infertility.

The other options do not correspond to long term consequences in adolescent women with STD's because

Condom use protects against STDs, but does not represent a long-term consequence.
The predisposition to contract HIV between 13 and 19 years old corresponds to male adolescents.
Not finding an STD-free partner should not be a long-term physical consequence.