Answer: Option A
Explanation:
When Andrew was exposed to the virus causing chicken pox he got infected and the virus crossed the blood brain barrier.
During the early stages when Andrew was a child there will be as such no effect of the virus in the brain.
During the early stage the virus will remain in the brain and cause harm in the later days when Andrew will be older.The virus can alter the brain functions such as homeostasis, blood brain barrier functions.It enters the brain while damaging the nervous system.
