Which of the following is true of human development?
a. Most organs begin to form during the second trimester.
b. Gastrulation takes place in the oviducts.
c. Genetic diseases can be detected by sampling cells from the chorion.
d. Implantation occurs through interactions of the zona pellucida with the uterine lining.
e. Exposure to drugs and chemicals is most likely to cause birth defects when it occurs in the third trimester.