Final answer:
Pregnancy tests detect the presence of the hCG hormone option (C), which is produced by the developing placenta during pregnancy.
Step-by-step explanation:
The correct answer is C. HCG hormone. Pregnancy tests detect the presence of human chorionic gonadotropin (hCG) hormone in urine or blood serum. hCG is produced by the developing placenta and is found in the urine and blood of pregnant individuals. The hormone can be detected using immunochromatographic assays, or lateral flow tests, which utilize antibodies that bind to hCG. When hCG is present, it forms a colored line on the test strip, indicating a positive result for pregnancy.