During childbirth, a hormone produced by the pituitary gland causes muscles of the mother's uterus (or womb) to contract. The more contractions there are, the more hormone is produced. Which best explains why this occurs?
A. Positive feedback is used to build more contractions.
B. Positive feedback is used to lessen the effects of the contractions.
C. Negative feedback is used to build more contractions.
D. Negative feedback is used to lessen the effects of the contractions.

Positive feedback is used to build more contractions.

Explanation:

Positive feedback mechanism in humans is also observed during childbirth which is induced by the pressing of the ovarian wall by the baby.

The pressing sensation is passed to the brain via different nerves, and in response, the brain stimulates the pituitary to produce oxytocin.

Oxytocin is responsible for the contractions of the uterine muscles which cause the movement of the fetus towards the cervix, further increasing the stimulus.  

The positive feedback loop continues until the baby is born.

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.

when the displaced particles are perpendicular to the direction the wave travels, is called a transverse wave, whereas in longitudinal wave the displace practices are parallel to the direction of the wave.

in the given image:

first image shows - longitudinal wave

second image shows - transverse wave

third image shows - longitudinal wave

fourth image shows - longitudinal wave