Teratogens: select one: a. are environmental agents that can harm the embryo or fetus. b. are most damaging during the fetal period of development. c. are only those substances the mother's body produces. d. harm the fetus only when taken in extremely large doses.

The answer is A. Teratogens are substances that impair the proper development of embryo or fetus. They include drugs, infections, radiation, and chemicals. The agents could cause the fetus to be physically or mentally impaired. Children born having been exposed to teratogens that affect their brain development could exhibit reduced IQ, communication challenges, and etcetera.

advantage of using stem cells in medical research:

1.       it provides medical benefits in the fields of therapeutic cloning and regenerative medicine.

2. it provides great potential for discovering treatments and cures to a variety of diseases including parkinson disease, spinal cord injuries, diabetes, alzheimer’s disease and many more.

3. limbs and organ could be grown in lab from stem cells and then used in transplant or treat illness.

the unequal cytoplasmic division that  results  in  one egg  and three polar bodies ensures that a fertilized  egg has  ample nutrients  forits journey  to  the uterus.