- A Chlamydia trachomatis (bacterium)
- B Chlamydia vaginalis (protozoan)
- C Chlamydia herpes (virus)
- D Chlamydia pallidum (spirochete)
Correct answer: A. Chlamydia trachomatis (bacterium)
Explanation: Chlamydia is caused by Chlamydia trachomatis, an obligate intracellular bacterium. It is one of the most common STIs and is often asymptomatic.
Concept context
Understand reproductive health, family planning, contraception methods, STIs, population control, and assisted reproductive technologies.