Final answer:
A urine test can detect pregnancy at as early as 2 weeks gestation, when the hormone hCG starts to be produced and is present in the urine.
Step-by-step explanation:
A urine test can positively indicate pregnancy as early as 2 weeks gestation, which corresponds to the option (a) 2 weeks gestation. At this stage, the body begins to produce the hormone human chorionic gonadotropin (hCG), which can be detected in urine. Most home pregnancy tests are designed to detect hCG soon after your period is missed, usually around the time of 4 to 5 weeks gestation, but some sensitive tests can detect it as early as 2 weeks gestation.