You are walking to school when you encounter a barking dog. you start sweating and contemplate whether you should run away. which nervous system is primarily responsible for this "fight-or-flight" reaction?

When any one encounter a stressful situation such as encounter of barking dog in this question. The stressful situation produces the “fight-or-flight” response. The hypothalamus stimulates the sympathetic nervous system and the adrenal gland. The sympathetic nervous system uses nerve pathways to initiate reactions in the body. Whereas, adrenal gland secretes hormone Adrenalin into the bloodstream. The combined effects of these two systems are the fight-or-flight response.

during the process of dna replication, brdu can replace thymidine and incorporate into the newly synthesized dna, cell proliferation thus can be reflected in the extent of brdu incorporation.

i think the answer is composed of atoms