Within cliques, the use of sarcasm and ridicule may

The myelin sheath and nodes of Ranvier are important because they _____

a) protect the neuron. b) speed neural impulses. c) create action potential. d) prevent refractory periods.

The germinal period of prenatal development begins with conception and ends about ___ later

a. one trimester b. two weeks c. one month d. 12 weeks