Researchers have been unable to pinpoint one cause of attention-deficit/hyperactivity disorder in children. there are several factors that can contribute to the existence of the disorder. not only might each of these factors have a direct impact on the disorder but they may interact with and affect each other in countless different ways. this is a good example of the of people that makes humans difficult to study.

Complexity

Explanation: Attention deficit hyperactivity disorder(ADHD) is a type of mental disorder .As this activity is related with the brain , the person having this disorder can behave in showing excessive activity, , not paying attention etc.

These are brain related acts which are not bound with the particular reason and symptoms as every person have different thoughts,response etc toward a certain situation . It could impact any person of any age due to several reason and can also affect others with such behavior .Thus ADHD is a case of complexity which is difficult to be analyzed and studied by human being.

abolish

do away with

unanimous

in complete agreement

secede

separate; break free

inauguration

starting a new position with a formal ceremony.

cooperationist

people who wanted the north to cooperate with the south

surrender

to give up

volunteer

perform a service for free

draft

involuntary service in military

retreat

withdraw; move away from enemy

advisor

expert who gives advice

explanation:

productive most commonly means: achieving or producing a significant amount or result.

explanation:

productive can also mean:

these depend on how the word productive is used. most likely productive will mean   achieving or producing a significant amount or result.