Most Teratogens Are Most Harmful to the Developing Fetus During

Multiple Choice

Most teratogens are most harmful to the developing fetus during the first trimester because

A) the fetus has not gathered sufficient resources to combat the effects of teratogens.
B) the placental barrier has not yet fully developed.
C) the fetal immune system is not yet capable of mounting a response to the teratogenic substance.
D) the first trimester contains the critical period of development for many major systems and body structures.