By the end of Gretas first month of pregnancy, her embryo __________.
A) can sense its world
B) is about inch long
C) can suck its thumb
D) can curl its toes
Question 2
The __________ folds over to form the __________, or primitive spinal cord.
A) mesoderm; neuron tract
B) ectoderm; neural tube
C) endoderm; neural tube
D) ectoderm; neuron tract