Final answer:
In true labor, the distinguishing feature is the dilation and effacement of the cervix, which is aided by regular, powerful, and increasingly frequent uterine contractions.
Step-by-step explanation:
The student has inquired about the difference between true and false labor. The true labor is characterized by several definitive signs. Notably, one sign of true labor is that the cervix will dilate and efface, meaning it will open and thin out in preparation for childbirth. During true labor, uterine contractions become regular, more powerful, and occur more frequently over time, aiding in the dilation and effacement of the cervix. These contractions represent a positive feedback loop where cervical stretching induces stronger uterine contractions that further dilate and efface the cervix, enhanced by the secretion of oxytocin which stimulates more powerful contractions. Therefore, the example of true labor from the options is that the cervix will dilate and efface.