The teratogen is a substance ingested by a pregnant woman that can cause a fetal abnormality. Any agent that can interrupt the growth of an embryo or fetus and may cause a birth deficiency in the child. The teratogen may stop the pregnancy downright. The types of teratogen comprise radiation, maternal contagions, compounds and drugs.<span />
        
             
        
        
        
I believe the answer is 16 calories
        
                    
             
        
        
        
Honestly I am not sure I will look into it!
And try and provide you a correct answer 
Good luck!
        
                    
             
        
        
        
Answer:
D. A signal is sent down an exon within a nerve cell
Explanation:
 
        
             
        
        
        
<span>The skull protects the brain and the vertebrae protects the spinal cord. The brain and spinal cord are wrapped in three layers of connective tissue called meninges. Between the meninges and the central nervous system tissue is a space filled withcerebrospinal fluid.</span>