The heart, lungs, and brain begin to form during the period of prenatal development. a. fetal b. zygotic c. embryonic d. blastocyst

c. embryonic

Explanation:

The embryonic period begins with the formation of the zygote, which after going through many cell divisions (mitoses), the cleavages, will attach to the walls of the uterus (nesting).

There new structures are formed (placenta, umbilical cord, among others), the organs and the gestation of the fetus begins until its birth during childbirth.

The process from fertilization to nesting lasts about a week, with the first division of the zygote occurring within 24 hours of fertilization.

 Ovulation corresponds to the first stage of embryonic development. When the ovary releases an egg (in fact it is a secondary oocyte) into the fallopian tube, the fertile period begins; If during the fertile period there is sexual contact and the sperm find the egg, one of them may be able to fertilize it. Otherwise, the woman will have her period and restart the menstrual cycle until ovulation again.

After fertilization of the egg there is union of nuclei and genetic content and formation of the zygote, which happens in the fallopian tube. Then the zygote goes through many divisions (mitoses) and travels to the uterus until it reaches the stage called blastocyst, when it will attach itself to the walls of the uterine endometrium, this is called nesting. If nesting is successful, embryo gestation will begin. If unsuccessful, the blastocyst will be eliminated during menstruation.

The embryo continues its development with the formation of chorion, amnion, allantoid and vitelline sac, whose functions are to protect, nurture and perform exchanges between the embryo and the external environment through the maternal body. After that, embryonic leaflets are formed, which are layers of cells that will originate the tissues and organs of the embryo. The process of organ formation is called organogenesis.

b - the respond is innate and varies over time.

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the cladogram shown here shows similarities and differences among several classes of vertebrates. anatomically, the four have limb structure as their common ancestor. we might separate the mammals from the other three classes because they a) divergent; do not lay eggs b) identical; are warm-blooded c) varied; a four chambered heart d) homologous; have mammary glands