**Core Concept**
Human pregnancy is confirmed by a combination of clinical signs and laboratory tests. Definitive signs of pregnancy indicate the presence of a viable intrauterine pregnancy.

**Why the Correct Answer is Right**
The definitive signs of pregnancy include a palpable uterus above the umbilicus, fetal heart sounds, and a positive pregnancy test. These signs confirm the presence of a viable intrauterine pregnancy.

**Why Each Wrong Option is Incorrect**
**Option A:** While amenorrhea (absence of menstruation) is often associated with pregnancy, it is not a definitive sign as it can be caused by various factors, including stress, weight changes, and certain medical conditions.
**Option C:** A positive beta-hCG test is a laboratory indicator of pregnancy, but it is not a definitive clinical sign as it can be influenced by various factors, including the sensitivity of the test and the timing of the sample collection.

**Clinical Pearl / High-Yield Fact**
Remember that a definitive diagnosis of pregnancy requires a combination of clinical signs and laboratory tests. A single positive test or clinical finding is not sufficient to confirm pregnancy.

**Correct Answer: B.**